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Asteroids

Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called “planetoids”. These terms have historically been applied to any astronomical object orbiting the Sun that did not show the disk of a planet and was not observed to have the characteristics of an active comet, but as minor planets in the outer Solar System were discovered, their volatile-based surfaces were found to resemble comets more closely and so were often distinguished from traditional asteroids. Thus the term asteroid has come increasingly to refer specifically to the small bodies of the inner Solar System out to a little beyond the orbit of Jupiter. They are grouped with the outer bodies–centaurs, Neptune trojans, and Trans-Neptunian Objects – as minor planets, which is the term preferred in astronomical circles.

Asteroids and the Asteroid Belt

The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. The asteroid belt is also termed the main asteroid belt or main belt to distinguish its members from other asteroids in the Solar System such as near-Earth asteroids and trojan asteroids. About half the mass of the belt is contained in the four largest asteroids, Ceres, Vesta, Pallas, and Hygiea. These have mean diameters of more than 400 km, while Ceres, the asteroid belt’s only dwarf planet, is about 950 km in diameter. The remaining bodies range down to the size of a dust particle. The asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident.

Several spacecraft flew by asteroids, some for gravity-assist “slingshots”, en route for other destinations:


Several spacecraft have visited asteroids as their primary objective. These are detailed below.

First Ring System Found around Asteroid: “10199 Chariklo” has Two Rings

Asteroid 10199 Chariklo lies within 0.09 AU of the 4:3 resonance of Uranus. This animation shows the motion of Chariklo in a rotating frame with a period equal to Uranus’s orbital period. The motion never halts and reverses course (i.e. librates). Uranus is the stationary blue line (rotating frame) at 4 o’clock, Saturn is yellow, and Jupiter is red. The animation consists of 79 frames covering 20,000 years. Many asteroids have orbits in resonance with a planet but the new discovery is that...

Chariklo

...this Asteroid has Two Rings (it’s called “(10199) Chariklo 1997 CU166”)


Artist Views of Chariklo

On 26th March 2014 astronomers at many of the European Southern Observatory sites, including the La Silla Observatory, made the surprise discovery that the remote asteroid 10199 Chariklo is surrounded by two dense and narrow rings. This is the smallest object by far found to have rings and only the fifth body in the Solar System – after the much larger planets Jupiter, Saturn, Uranus and Neptune – to have this feature. The origin of these rings remains a mystery, but they may be the result of a collision that created a disc of debris. The new results were published online in the journal Nature on 26th March 2014.

All objects that orbit the Sun, which are too small (not massive enough) for their own gravity to pull them into a nearly spherical shape are now defined by the IAU as being small solar system bodies. This class currently includes most of the Solar System asteroids, near-Earth objects (NEOs), Mars and Jupiter Trojan asteroids, most Centaurs, most Trans-Neptunian objects (TNOs), and comets. In informal usage the words asteroid and minor planet are often used to mean the same thing.

The IAU Minor Planet Center is the nerve centre for the detection of small bodies in the Solar System. The names assigned are in two parts, a number – originally the order of discovery but now the order in which orbits are well-determined – and a name.

10199 Chariklo is the largest known centaur, with an absolute magnitude of 6.4. It orbits the Sun between Saturn and Uranus, grazing Uranus. It was discovered on 15th February 1997 by James V. Scotti; the rings may be partially composed of water ice.

The rings of Saturn are one of the most spectacular sights in the sky, and less prominent rings have also been found around the other giant planets. Despite many careful searches, no rings had been found around smaller objects orbiting the Sun in the Solar System. Now observations of the distant minor planet (10199) Chariklo as it passed in front of a star have shown that this object too is surrounded by two fine rings.

“We weren’t looking for a ring and didn’t think small bodies like Chariklo had them at all, so the discovery – and the amazing amount of detail we saw in the system – came as a complete surprise!” says Felipe Braga-Ribas (Observatório Nacional/MCTI, Rio de Janeiro, Brazil) who planned the observation campaign and is lead author on the new paper.

Predictions had shown that it would pass in front of the star UCAC4 248-108672 on 3rd June 2013, as seen from South America. The event was predicted following a systematic search conducted with the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory and recently published. Astronomers using telescopes at seven different locations, including the 1.54-metre Danish and TRAPPIST telescopes at ESO’s La Silla Observatory in Chile, were able to watch the star apparently vanish for a few seconds as its light was blocked by Chariklo – an occultation. This is the only way to pin down the precise size and shape of such a remote body – Chariklo is only about 250 km in diameter and is more than a billion kilometres from Earth. Even in the best telescopic views such a small and distant object just appears as a faint point of light.

Besides the Danish 1.54-metre and TRAPPIST telescopes at La Silla, event observations were also performed by the following observatories: Universidad Católica Observatory (UCO) Santa Martina operated by the Pontifícia Universidad Católica de Chile (PUC); PROMPT telescopes, owned and operated by the University of North Carolina at Chapel Hill; Pico dos Dias Observatory from the National Laboratory of Astrophysics (OPD/LNA) – Brazil; Southern Astrophysical Research (SOAR) telescope; Caisey Harlingten’s 20-inch Planewave telescope, which is part of the Searchlight Observatory Network; R. Sandness’s telescope at San Pedro de Atacama Celestial Explorations; Universidade Estadual de Ponta Grossa Observatory; Observatorio Astronomico Los Molinos (OALM) – Uruguay; Observatorio Astronomico, Estacion Astrofisica de Bosque Alegre, Universidad Nacional de Cordoba, Argentina; Polo Astronômico Casimiro Montenegro Filho Observatory and Observatorio El Catalejo, Santa Rosa, La Pampa, Argentina.

But they found much more than they were expecting. A few seconds before, and again a few seconds after the main occultation there were two further very short dips in the star’s apparent brightness. Something around Chariklo was blocking the light! By comparing what was seen from different sites the team could reconstruct not only the shape and size of the object itself but also the shape, width, orientation and other properties of the newly discovered rings. The team found that the ring system consists of two sharply confined rings only seven and three kilometres wide, separated by a clear gap of nine kilometres – around a small 250-kilometre diameter object orbiting beyond Saturn. The rings of Uranus, and the ring arcs around Neptune, were found in a similar way during occultations in 1977 and 1984, respectively. ESO telescopes were also involved with the Neptune ring discovery.


An artist’s impressions of space rock Chariklo

Comparison of Chariklo, Pluto and the Moon, based on mean radius

“For me, it was quite amazing to realise that we were able not only to detect a ring system, but also pinpoint that it consists of two clearly distinct rings,” adds Uffe Gråe Jørgensen (Niels Bohr Institute, University of Copenhagen, Denmark), one of the team. “I try to imagine how it would be to stand on the surface of this icy object – small enough that a fast sports car could reach escape velocity and drive off into space – and stare up at a 20-km wide ring system 1000 times closer than the Moon.” (Strictly speaking the car would have to be rather fast – something like a Bugatti Veyron 16.4 or McLaren F1 – as the escape velocity is around 350 km/hour!) Although many questions remain unanswered, astronomers think that this sort of ring is likely to be formed from debris left over after a collision. It must be confined into the two narrow rings by the presence of small putative satellites. “So, as well as the rings, it’s likely that Chariklo has at least one small moon still waiting to be discovered,” adds Felipe Braga Ribas. There are several such moons, known as “shepherding moons” in the rings of Saturn.

The rings may prove to be a phenomenon that might in turn later lead to the formation of a small moon. Such a sequence of events, on a much larger scale, may explain the birth of our own Moon in the early days of the Solar System, as well as the origin of many other satellites around planets and asteroids.

The leaders of this project are provisionally calling the rings by the nicknames Oiapoque and Chuí, two rivers near the northern and southern extremes of Brazil. These names are only for informal use, the official names will be allocated later by the IAU, following pre-established rules.

More information from Science Daily

Some Interesting Asteroids

Asteroids Asteroids

This representation of the physical properties of some interesting asteroids includes most of the asteroids larger than about 200 km in diameter. They are portrayed in their correct relative sizes and shapes (the limb of Mars is shown for comparison); colours and albedos (the proportion of sunlight they reflect) are also indicated. The bodies are positioned at their correct relative distances from the Sun.

Asteroids located near the top or bottom of the diagram occupy relatively eccentric or inclined orbits (or both), while those shown near the ecliptic plane move in relatively circular, non-inclined orbits.

Rotation periods, in hours, are given in the lower panel.

The Flora Family

Among the special smaller asteroids indicated are members of the Flora families larger than 15 km in diameter, but this illustration would be hopelessly cluttered if all asteroids of comparable size were shown — an estimated 1,150 asteroids in the main belt alone have diameters larger than 30 km, yet only five Flora-family asteroids attain that size.

The Flora-family of asteroids may be the source of the Chicxlub (Cretaceous–Paleogene) impactor, the likely culprit in the extinction of the dinosaurs, believed to have been at least 10 km in diameter. (It’s a sobering thought that such a small object could have caused such a catastrophe.)

Asteroid 4179 Toutatis


Toutatis

Asteroid 4179 Toutatis is particularly interesting, because it approached the Earth to within four times the Moon’s distance in 2004. It’s irregular in shape, with dimensions 4.5×2.4×1.9 km, and mass 5.0×1013 kg.
[It is too small to be depicted in this diagram]

Asteroid 624 Hektor


Asteroid Hektor

Note, in the upper right of the diagram, the contact-binary Trojan asteroid (624) Hektor, the largest of the Flora group.

An 8-minute exposure of Jupiter Trojan 624 Hektor with a 24-inch telescope. Hektor is apparent magnitude 15.0 in this image taken on 29th September 2009 at 10:00 UTC. The bright star blooming above asteroid Hektor is TYC 2351-444-1 at magnitude 9.9 (about the limit of typical 50mm binoculars). The star on the right of the bloom that is comparable to Hektor is of magnitude 14.8. The star to the far lower left of Hektor (showing very mild blooming) is of magnitude 12.7.


And don’t forget 2012 DA14, now named (367943) Duende, and the Chelyabinsk meteorite.


Mining Asteroids

Mining Asteroids

A group of hi-tech tycoons including Google’s Larry Page and Eric Schmidt teamed up with explorer and film-maker James Cameron in a venture to mine nearby asteroids. In this artist’s impression an astronaut tethers an asteroid. A space exploration vehicle is close by and an Orion crew vehicle can be seen docked to a habitat in the background. (Once you’ve fouled up your own back yard, go and find another!)

Asteroid Density

Resonance with Jupiter

The graph shows the number density of asteroids as a function of their distance from the Sun. Note that there are peaks and troughs in this density due to exact periodic resonance with Jupiter. Also, the peak above 5 AU is due to the Trojan asteroids. These asteroids are located approximately at the leading and trailing Lagrangian (or trojan) points of Jupiter’s orbit.

Jupiter is an enormous part of the mass of the solar system, apart from the Sun itself. As a result, over the billions of years of the existence of the system, it has influenced the paths of many of the smaller objects (and some of the larger ones) so that asteroids finding themselves in a resonant obit with Jupiter may have been flung out of their orbits into ones that are more stable. Alternatively they may have been flung out of orbit to collide with other objects (planets, moons, etc.)

Some asteroids may have ended up in orbits that resonate with Jupiter’s, and find themselves in stable environments. Many of these are the so-called Trojan groups, at one or other of the Lagrange points associated with Jupiter. Such stable orbits are also associated with other planets.

Two of the stories that I have written have strong ‘solar system’ references. Try reading them:

  • The Plutonian — a Science Fiction story set in about the year 2500
  • The Green Flash — a longer Science Fiction story set in the present (written in summer 2011)

Main Asteroid Types

There is a class of asteroids for almost every letter of the alphabet, but these are the more interesting or more common types.

C-type
carbonaceous asteroids, they are the most common variety, forming around 75% of known asteroids, and an even higher percentage in the outer part of the asteroid belt beyond 2.7 AU, which is dominated by this asteroid type. The proportion may actually be greater than this, because C-types are much darker than most other asteroid types except D-types and others common only at the extreme outer edge of the asteroid belt.
M-type
asteroids of partially known composition; they are moderately bright (albedo 0.1–0.2). Some, but not all, are made of nickel-iron, either pure or mixed with small amounts of stone. These are thought to be pieces of the metallic core of differentiated asteroids that were fragmented by impacts, and are thought to be the source of iron meteorites. They are the third most common type.
K-type
asteroids are relatively uncommon with a moderately reddish spectrum shortwards of 0.75 μm, and a slight bluish trend longwards of this; they have a low albedo.
L-type
asteroids are relatively uncommon with a strongly reddish spectrum shortwards of 0.75 μm, and a featureless flat spectrum longwards of this. In comparison with the K-type, they exhibit a more reddish spectrum at visible wavelengths and a flat spectrum in the infrared.
R-type
asteroids are moderately bright, relatively uncommon inner-belt asteroids that are spectrally intermediate between the V- and A-types. The spectrum shows distinct olivine and pyroxene features at 1 and 2 μm, with a possibility of plagioclase. Shortwards of 0.7 μm the spectrum is very reddish.
S-type
asteroids are of a stony composition, hence the name. Approximately 17% of asteroids are of this type, making it the second most common.
V-type
asteroids (or Vestoids) are similar to 4 Vesta, by far the largest asteroid in this class (hence the name). Most have orbital elements similar to Vesta’s, either close enough to be part of the Vesta family, or with similar eccentricities and inclinations but with a semi-major axis lying between about 2.18 AU and the 3:1 Kirkwood gap at 2.50 AU. This suggests that most or all of them originated as fragments of Vesta’s crust, possibly blasted out by a single very large impact. The enormous southern-hemisphere crater on Vesta is the prime candidate for the impact site.
These asteroids are moderately bright, and rather similar to the more common S-type, which are also made up of stony irons and ordinary chondrites but containing more pyroxene than the S-type. The electromagnetic spectrum has a very strong absorption feature longward of 0.75 μm, another feature around 1 μm and is very red shortwards of 0.7 μm.

Asteroid 25143 Itokawa

Tiny Asteroid Itokawa, visited by a Japanese spacecraft

Black and white image of Asteroid 25143 Itokawa (dimensions 535×294×209 m) as observed by the Japanese spacecraft Hayabusa-1.

Asteroid 21 Lutetia

Asteroid 21 Lutetia as seen by Rosetta

Asteroids 243 Ida and Dactyl

Asteroids Ida and its Moon Dactyl

Some Asteroids to Scale

Some Asteroids to Scale

On the left is another composite image, to scale this time, of the asteroids that have been imaged at high resolution.
They are, from largest to smallest:

The ‘Missing’ Planet

In the late 18th Century, Titius and Bode noted a sequence in the distances of the planets from the Sun, which became known as the Titius–Bode Law or just Bode’s Law. They noted “...the astonishing relation which the known six planets observe in their distances from the Sun. Let the distance from the Sun to Saturn be taken as 100, then Mercury is separated by 4 such parts from the Sun. Venus is 4+3=7. The Earth 4+6=10. Mars 4+12=16. Now comes a gap in this so orderly progression, at 4+24=28 parts, in which no planet has yet been seen. From here we come to the distance of Jupiter by 4+48=52 parts, and finally to that of Saturn by 4+96=100 parts.”

It was regarded as interesting, but of no great importance until the discovery of Uranus in 1781 which happens to fit neatly into the series. Based on this discovery, Bode urged a search for a fifth planet. Ceres, the largest object in the asteroid belt, was found at Bode’s predicted position in 1801. Bode’s law was then widely accepted until Neptune was discovered in 1846 and found not to satisfy Bode’s law. Simultaneously, the large number of known asteroids in the belt resulted in Ceres (and its large neighbours, Pallas, Juno, and Hygiea) no longer being considered a planet at that time.

The discovery of Pluto in 1930 confounded the issue still further. While nowhere near its position as predicted by Bode’s law, it was roughly at the position the law had predicted for Neptune.

Attributes of Protoplanetary Asteroids
Name Orbital radius Orbital period Inclination to ecliptic Orbital eccentricity Diameter
(km)		 Diameter
(% of Moon)
4 Vesta 2.36 AU 3.63 years 7.1° 0.089 573×557×446 (mean 525) 15%
1 Ceres 2.77 AU 4.60 years 10.6° 0.079 975×975×909 (mean 952) 28%
2 Pallas 2.77 AU 4.62 years 34.8° 0.231 580×555×500 (mean 545) 16%
10 Hygiea 3.14 AU 5.56 years 3.8° 0.117 530×407×370 (mean 430) 12%
Name Mass
(×1018 kg)		 Mass
(% of Ceres)		 Density
(g/cm3)		 Rotation
period (hr)		 Axial
tilt		 Surface
temperature
4 Vesta 260 28% 3.44 ± 0.12 5.34 29° 85–270 K
1 Ceres 940 100% 2.12 ± 0.04 9.07 ≈3° 167 K
2 Pallas 210 22% 2.71 ± 0.11 7.81 ≈80° 164 K
10 Hygiea 87 9% 2.76 ± 1.2 27.6 ≈60° 164 K

Main-Belt Asteroids

The main asteroid belt (with an estimated 750,000 asteroids larger than 1 km in diameter and millions of smaller ones) is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies (asteroids or minor planets). The asteroid belt is also termed the main asteroid belt or main belt to distinguish its members from other asteroids in the Solar System such as near-Earth asteroids and trojan asteroids. About half the mass of the belt is contained in the four largest asteroids, Ceres, Vesta, Pallas, and Hygiea. These have mean diameters of more than 400 km, while Ceres, the asteroid belt’s only dwarf planet, is about 950 km in diameter. The remaining bodies range down to the size of a dust particle. The asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids do occur, and these can form an asteroid family whose members have similar orbital characteristics and compositions. Nesvorny and Jenniskens (2010 Astrophysical Journal) attributed 85% of the Zodiacal Light dust to fragmentations of Jupiter-family comets, rather than from comets and collisions between asteroids in the asteroid belt. It was once thought that collisions of asteroids produce a fine dust that forms a major component of the zodiacal light. Individual asteroids within the asteroid belt are categorized by their spectra, with most falling into three basic groups [see types]: carbonaceous (C-type), silicate (S-type), and metal-rich (M-type).

Inner/Mid Solar System Asteroids

Apollos

The Apollo asteroids (4,662 recorded) are a group of near-Earth asteroids named after 1862 Apollo, the first of this group to be discovered. They are Earth-crosser asteroids that have orbital semi-major axes greater than that of the Earth (more than 1 AU) and a perihelion distance less than 1.017 AU. Some can get very close to the Earth, making them a potential threat to our planet (the closer their semi-major axis is to Earth’s, the less eccentricity is needed for the orbits to cross). The largest known Apollo asteroid is 1866 Sisyphus, with a diameter of about 10 km.

Amors

The Amor asteroids (3,947 recorded) are a group of near-Earth asteroids named after 1221 Amor. They approach the orbit of the Earth from beyond, but do not cross it. Most Amors do cross the orbit of Mars. The two moons of Mars, Deimos and Phobos, may be Amor asteroids that were captured by Mars’s gravity. The most famous member of this group is 433 Eros, which was the first asteroid to be orbited and then landed upon by a human probe (NEAR Shoemaker).

Hungarias

The Hungaria asteroids (11,490 recorded) are a group of asteroids in the asteroid belt that orbit the Sun between 1.78 and 2.00 AU. The asteroids typically have a low eccentricity (below 0.18) and an inclination of 16 to 34°. They have an orbital period of approximately 2.5 years. They have a resonance with Jupiter of 9:2 and with Mars of 3:2. They are named after the largest member, 434 Hungaria which is only about 20 km in size, and are the innermost dense concentration of asteroids, lying somewhat inwards of the “core” of the asteroid belt that lies beyond the 4:1 Kirkwood gap.

Most Hungarias are E-type asteroids, which means they have extremely bright enstatite surfaces and albedos typically above 0.30. Despite their high albedos, none can be seen with binoculars because they are far too small; they are, however, the smallest asteroids that can regularly be glimpsed with amateur telescopes.

The origin of the Hungaria group of asteroids is well known. At the 4:1 orbital resonance with Jupiter that lies at semi-major axes of 2.06 AU, any orbiting body is sufficiently strongly perturbed to be forced into an extremely eccentric and unstable orbit, creating the innermost Kirkwood gap. Interior to this 4:1 resonance, asteroids in low inclination orbits are, unlike those outside the 4:1 Kirkwood gap, strongly influenced by the gravitational field of Mars. Here, instead of Jupiter’s influence, perturbations by Mars have, over the lifetime of the Solar System, thrown out all asteroids interior to the 4:1 Kirkwood gap except for those far enough from Mars’s orbital plane where that planet exerts much smaller forces.

This has left a situation where the only remaining concentration of asteroids inward of the 4:1 resonance lies at high inclination orbits, although they have fairly low eccentricities. However, even at the present time in Solar System history some Hungaria asteroids cross the orbit of Mars and in the process of still being ejected from the solar system due to Mars’s influence (unlike asteroids in the “core” of the asteroid belt, where Jupiter’s influence predominates).

Aten Asteroids

Aten

The Aten asteroid group (shown as a green cloud); the planets here are Mercury, Venus, Earth and Mars (and the pale blue clouds in Mars’s orbit are its Trojans)

The Aten asteroids (727 recorded) are a group of near-Earth asteroids, named after the first of the group to be discovered (2062 Aten, found in 1976). They are defined by having semi-major axes of less than one astronomical unit (the distance from the Earth to the Sun). Because asteroids’ orbits can be highly eccentric, an Aten orbit need not be entirely contained within Earth’s orbit; in fact, nearly all known Aten asteroids have their aphelion greater than one AU even though their semi-major axis is less than one AU. Observation of objects inferior to the Earth’s orbit is difficult and may be the cause of some bias in the apparent preponderance of eccentric Atens.

The Aten asteroid with the smallest known perihelion is also the one with the highest known eccentricity: (137924) 2000 BD19 has an orbit with an eccentricity of 0.895, which takes it from a perihelion of 0.092 AU, well within Mercury’s orbit, to an aphelion of 1.661 AU.

Apohele and Atira Asteroids

Asteroids that have their aphelion entirely within the Earth’s orbit (18 recorded) are known as Apohele asteroids (the Hawaiian word for “orbit”, apparently as if formed from the words “apoapsis” and “helios”), or as Inner Earth Objects (IEOs) or Atira asteroids ((163693) Atira was the first such to be confirmed). Apoheles are traditionally treated as a subclass of Atens, but sometimes are separated. As of August 2012, there are only eleven known Apoheles, and 716 more known Aten asteroids. The smallest aphelion is that of 2008 EB26, at 0.804 AU. The shortest semi-major axis for any known Aten asteroid is that of another Apohele, 2007 EA32, at 0.550 AU.

99942 Apophis and Similar Asteroids

For a brief time near the end of 2004, the asteroid 99942 Apophis (then known only by its provisional designation 2004 MN4) appeared to pose a threat of causing an Earth impact event in 2029, but earlier observations were found that eliminated that possibility, although a very small possibility remains for 2036. [Apophis was an evil god in ancient Egyptian religion, the deification of darkness and chaos, and the opponent of light, order and truth.]

The orbit and size of 99942 Apophis have recently been revised; it is now believed to be 325 m in diameter. Its probability of an impact with the Earth on [yes] Friday the 13th April 2029 is 1 in 133,000. It may, however hit the Earth in 2036, though, for many reasons, the probability of that happening are much less certain; the latest calculated probability of an impact on 13th April 2036 (a Sunday) is 1 in 7,143,000, as reported at its most recent close approach to the Earth on 9th January 2013. If it does hit the Earth in 2036, its impact may be of the order of 510 megatons of TNT (the Krakatoa eruption was about 200 megatons and the biggest H-bomb exploded was about 50 megatons). Its impact path is predicted to cross southern Russia, the Pacific Ocean, close to California and Mexico, across Nicaragua or Costa Rica and then the Atlantic, stopping short before Africa. If it hits land tens of millions of people might be killed, and if it lands in either ocean, a giant tsunami would result causing huge devastation. Wikipedia, NASA’s Near Earth Object Program and the news media will have more information as “doomsday” approaches. It is being monitored by the B612 Foundation whose Sentinel mission aims to build, launch, and operate the first privately funded deep space mission – a space telescope to be placed in orbit around the Sun.

Asteroid 280 Philia

This may sound a strange excuse for including a couple of photographs of the sky, but bear with me.

Asteroid 280 Philia Asteroid 280 Philia

About Asteroid 280 Philia

I was looking up words ending in -philia and -phobia – I sometimes get obsessed with lists of things – and I came across phobialist.com and a web-site of -philias.

Then I wondered if there were any astronomical objects called “Philia”, “Phobia” or something similar. The obvious starter is Phobos, a moon of the planet Mars [Apart from my account of Phobos, Wikipedia has a lot more]. The other one I found is Asteroid 280 Philia. I’d never heard of it before, and, as far as I’m aware, there is nothing special about it.

280 Philia is a fairly large main belt asteroid with an aphelion of 487.353 Gm (3.258 AU), a perihelion of 393.613 Gm (2.631 AU), a semi-major axis of 440.483 Gm (2.944 AU) and an orbital eccentricity of 0.106; its orbital period is 1845.459 days (5.05 years). The asteroid’s diameter is 46.0 km, but its mass, mean density, equatorial surface gravity, escape velocity, rotation period, albedo, temperature, and spectral type are all unknown. Its absolute magnitude (H) is 10.7. It is named after the Ancient Greek Φιλία, often translated “brotherly love”, one of the four ancient Greek words for love. Philia in Aristotle’s Nicomachean Ethics is usually translated as affectionate regard or “friendship”.

The two charts shown above are accompanied with text in Japanese, but I think they are to do with the occultation of star TYC 0026-01163-1 by asteroid 280 Philia. Note that the two charts are to different scales.

280 Philia was discovered by Johann Palisa (1848 – 1925) on 29th October 1888 at the Vienna Observatory. He was an Austrian astronomer, born in Troppau in Austrian Silesia (now in the Czech Republic).

From 1866 to 1870, Palisa studied mathematics and astronomy at the University of Vienna; however, he did not graduate until 1884. Despite this, by 1870 he was an assistant at the University’s observatory, and a year later gained a position at the observatory in Geneva. A few years later, in 1872, at the age of 24, Palisa became the director of the Austrian Naval Observatory in Pula. While at Pula, he discovered his first asteroid, named 136 Austria for obvious reasons, on 18th March 1874. Along with this, he discovered twenty-seven minor planets and one comet. During his stay in Pula he used a small six-inch refractor telescope to aid in his research. He was awarded the Lalande Prize in 1876.

He was a prolific discoverer of asteroids, discovering 122 in all (listed here), from 136 Austria in 1874 to 1073 Gellivara in 1923. Some of his notable discoveries include 153 Hilda, 216 Kleopatra, 243 Ida, 253 Mathilde, 324 Bamberga, and the Amor asteroid 719 Albert. The asteroid 914 Palisana and the crater Palisa on the Moon were named in his honour.

Other Spacecraft that Flew by Asteroids, Some for “Slingshots”

As well as the spacecraft described below, these craft passed close to asteroids; some of them gained gravity assistance by these flybys.

The Largest Asteroids

  1. Ceres is a ball of rock and ice 950 km in diameter, containing a third of the mass of the asteroid belt. It is the largest asteroid, and the only dwarf planet in the inner Solar System. It was the first asteroid to be discovered, on 1st January 1801 by Giuseppe Piazzi. The unmanned Dawn spacecraft is scheduled to arrive at Ceres in early 2015.
  2. Pallas was discovered on 28th March 1802, and is estimated to comprise 7% of the mass of the asteroid belt; its diameter of 544 km is slightly larger than that of 4 Vesta. Pallas is 10 to 30% less massive than Vesta, placing it third among the asteroids. It is possibly the largest irregularly shaped body in the Solar System (that is, the largest body not rounded under its own gravity) and a remnant protoplanet.
  3. Juno was the third asteroid to be discovered and is one of the larger main-belt asteroids, being one of the two largest stony (S-type) asteroids, along with 15 Eunomia. It is estimated to contain 1% of the total mass of the asteroid belt. Juno was discovered on 1st September 1804.

  4. Composite greyscale image of Vesta taken by the Dawn spacecraft
    Vesta is one of the largest asteroids in the Solar System, mean diameter 525 km. It was discovered on 29th March 1807. Vesta is the second most massive asteroid after Ceres, and comprises an estimated 9% of the mass of the asteroid belt. Vesta is the last remaining rocky protoplanet (with a differentiated interior) of the kind that formed the terrestrial planets. Numerous fragments of Vesta were ejected by collisions one and two billion years ago, leaving two enormous craters occupying much of Vesta’s southern hemisphere. Debris from these events have fallen to Earth as howardite–eucrite–diogenite (HED) meteorites, which have been a rich source of information about Vesta. NASA’s Dawn spacecraft entered orbit around Vesta on 16th July 2011 for a one-year exploration and left on 5th September 2012 heading for Ceres. NASA has also released results from the Dawn mission about Vesta. This asteroid was believed to be dry, since it was thought that asteroids are incapable of retaining water. Yet there is evidence that Vesta may have had short-lived flows of water-mobilised material on its surface. These results make the asteroid very interesting as these characteristics were thought only to be present on planets.
  5. Hygiea is the fourth largest asteroid in the Solar System by volume and mass, and it is in the main asteroid belt. With somewhat oblong diameters of 350–500 km and a mass estimated to be 2.9% of the total mass of the belt, it is the largest of the class of dark C-type asteroids with a carbonaceous surface. Despite its size, it appears very dim when observed from Earth. This is due to its dark surface and larger than average distance from the Sun. For this reason, several smaller asteroids were observed before Hygiea on 12th April 1849.
  6. Interamnia
    Observation of 704 Interamnia at the Observatory of Teramo, Italy, on the 101st anniversary of its discovery
    Interamnia is a very large asteroid, with an estimated diameter of 350 km. Its mean distance from the Sun is 3.067 AU. It was discovered on 2nd October 1910. Interamnia is probably the fifth most massive asteroid after Ceres, Vesta, Pallas, and Hygiea, with a mass estimated to be 1.2% of that of the entire asteroid belt. Its apparently high bulk density (though subject to much error) suggests an extremely solid body entirely without internal porosity or traces of water. This also strongly suggests that it is large enough to have fully withstood all the collisions that have occurred in the asteroid belt since the Solar System was formed.

Mars-Crossing Asteroids

A Mars-crosser (8970 recorded) is an asteroid whose orbit crosses that of Mars. They include the two numbered Mars trojans 5261 Eureka and (101429) 1998 VF31.

Many databases, for instance the Jet Propulsion Laboratory’s online Small-Body Database Browser, only list asteroids with a perihelion greater than 1.3 AU as Mars-crossers. An asteroid with a perihelion less than this is classed as a near-Earth object instead, even though it is crossing the orbit of Mars as well as crossing (or coming near to) that of Earth. A grazer is an object with a perihelion below the aphelion of Mars (1.67 AU) but above the Martian perihelion (1.58 AU).

Asteroid 87 Sylvia and its satellites Romulus and Remus

Asteroids Sylvia, Romulus and Remus
Adaptive Optics observations of 87 Sylvia, showing its two satellites, Remus and Romulus

87 Sylvia was discovered in 1866, and is a Cybele group asteroid in the outer main belt. It is one of the largest main-belt asteroids and is the first asteroid known to possess more than one moon. Sylvia is very dark in colour and probably has a very primitive composition. The discovery of its moons made possible an accurate measurement of the asteroid’s mass and density. Its density was found to be very low (around 1.2 times the density of water), indicating that the asteroid is porous to very-porous; from 25% to as much as 60% of it may be empty space, depending on the details of its composition. However, the mineralogy of the “X-type” asteroids is not known well enough to constrain this further. Either way, this suggests a loose rubble pile structure. Sylvia is also a fairly fast rotator, turning about its axis every 5.18 hours (giving an equatorial rotation velocity of about 230 km/h). The short axis is the rotation axis. Direct images indicate that Sylvia’s pole points towards ecliptic coordinates (+62.6°, 72.4°) with only a 0.5° uncertainty, which gives it an axial tilt of around 29.1°. Sylvia’s shape is strongly elongated.

Sylvia has two orbiting satellites. They have been named (87) Sylvia I Romulus and (87) Sylvia II Remus, after Romulus and Remus, the children of the mythological Rhea Silvia. Romulus was discovered on 18th February 2001 from the Keck II telescope. Remus was discovered over three years later on 9th August 2004 using the Yepun telescope of the European Southern Observatory (ESO) in Chile.

The orbital properties of the satellites are given here. The orbital planes of both satellites and the equatorial plane of the primary asteroid are all well-aligned within about 1° of each other, suggesting the satellites were formed in or near the equatorial plane of the primary. Remus has a mass of 7.3×1014 kg, a semi-major axis of 706.5 km, an orbital period of 1.37 days, and an orbital eccentricity of 0.027. The corresponding data for Romulus are: 9.3×1014 kg, 1357 km, 3.65 days, and 0.006.

Romulus (dimensions 18±4 km), the outer and larger moon of Sylvia, (not to be confused with the directly Sun-orbiting asteroid 10386 Romulus) and Remus (dimensions 7±2 km), the inner and smaller moon, both follow an almost-circular close-to-equatorial orbit around the parent asteroid.

Like 87 Sylvia, Romulus and Remus are probably smaller rubble piles which accreted in orbit around the main body from debris of the collision that resulted in Sylvia. In this case their albedo and density are expected to be similar to Sylvia’s. Romulus’ and Remus’ orbits are expected to be quite stable – they lie far inside Sylvia’s Hill sphere (about 1/50 of Sylvia’s Hill radius for Romulus, about 1/100 for Remus), but also far outside the synchronous orbit.

Hildas

The Hilda or Hildian asteroids are a dynamical group of asteroids in a 3:2 orbital resonance with Jupiter. Hildas move in their elliptical orbits so that their aphelia put them opposite Jupiter, or 60° ahead of or behind Jupiter at the L4 and L5 Lagrangian points. Over three successive orbits each Hilda asteroid passes through all of these three points in sequence. Consequently, a Hilda’s orbit has a semi-major axis between 3.7 AU and 4.2 AU, an eccentricity less than 0.3, and an inclination less than 20°. They do not form a true asteroid family, in the sense that they do not descend from a common parent object. The namesake is 153 Hilda, discovered in 1875. There are more than 3,799 recorded Hilda asteroids including unnumbered objects.

Hildas’ surface colours often correspond to the low-albedo D-type and P-type; however, a small portion are C-type. D-type and P-type asteroids, such as Hildas and Trojans found in the outer main asteroid belt, have surface colours, and thus also surface mineralogies, similar to those of cometary nuclei. This implies that they share a common origin.

Asteroid 3208 Lunn: Discovery

I couldn’t resist including this asteroid, for purely selfish reasons – asteroid 3208 Lunn (1981 JM) is a main-belt asteroid (SPK-ID: 2003208). This section shows the enormous amount of information that is available for such a minor, insignificant object.

The asteroid was discovered at the Anderson Mesa (AM) (688) station, which is operated by the Lowell Observatory, Flagstaff, Arizona (see also Wikipedia). The Anderson Mesa station was established in 1959 as a dark-sky observing site for Lowell Observatory; it is located in Coconino County, Arizona (USA), about 12 miles southeast of Lowell’s main campus on Mars Hill in Flagstaff, Arizona. It was found on 3rd May 1981 by E. Bowell. Edward L. G. “Ted” Bowell, born in 1943 in London, an American astronomer, educated at Emanuel School London, University College, London, and the Université de Paris. He was principal investigator of the Lowell Observatory Near-Earth-Object Search (LONEOS). He has discovered a large number of asteroids (572), both as part of LONEOS and in his own right before LONEOS began. Among the latter are the Trojan asteroids 2357 Phereclos, 2759 Idomeneus, 2797 Teucer, 2920 Automedon, 3564 Talthybius, 4057 Demophon, and (4489) 1988 AK. He also co-discovered the periodic comet 140P/Bowell-Skiff and the non-periodic comet C/1980 E1.

3208 Lunn: STARDUST Spacecraft Microchip Names

As a public outreach effort, over 1 million names were collected and engraved on the STARDUST spacecraft, which visited Comet Wild 2 in 2004. Some of the names on the chip:
...LUNN, AMANDA L LUNN, ASTEROID 3208 LUNN, BEVERLY L LUNN, CHRISTOPHER M LUNN, CLAUDIA LUNN, GRAEME LUNN, JACQUELINE E LUNN, JOAN M LUNN, JOY E LUNN, KENNETH R LUNN, KEVIN B LUNN, LAYNE LUNN, MICHELLE R LUNN, NICHOLAS LUNN, ROBERT J LUNN, RON L LUNN, RONNIE J LUNN, ROSE LUNN...

3208 Lunn: Orbital Characteristics (epoch 14th May 2008)

Data is from JPL: Orbital Elements at Epoch 2456600.5 (2013-Nov-04.0) TDB (Barycentric Dynamical Time), Reference: JPL 3 (heliocentric ecliptic J2000). Uncertainties are 1-sigma values.

Aphelion: 3.444421154835977 AU (uncertainity 2.9687×10-8)
Perihelion: 2.801024338437844 AU (uncertainity 2.316×10-7)
Argument of perihelion: 26.57350850853789° (uncertainity 0.00014861°)
Time of perihelion passage: 2456505.642790259796 JED (Julian Ephemeris Date) (2013-Aug-01.14279026) (uncertainity 0.00016629)
Semimajor axis: 3.12272274663691 AU (uncertainity 2.6915×10-8)
Eccentricity: 0.1030185624213763 (uncertainity 7.3648×10-8)
Orbital period: 2015.573162329727 days (uncertainity 2.6058×10-5 days); 5.52 years (uncertainity 7.134×10-8)
Inclination to the ecliptic: 2.335585810873711° (uncertainity 6.4453×10-6)
Longitude of ascending node: 136.5846013889574° (uncertainity 0.00014556°)
Mean motion: 0.1786092446199717°/day (uncertainity 2.3091×10-9)
Mean anomaly: 16.942374578456° (uncertainity 2.9719×10-5)
[The mean anomaly is a parameter relating position and time for an orbiting body; it is based on the fact that equal areas are swept in equal intervals of time by a line joining the focus and the orbiting body (Kepler’s second law). The mean anomaly increases uniformly from 0 to 2π radians during each orbit; however, it is not an angle – the mean anomaly is proportional to the area swept by the focus-to-body line since the last periapsis (the point of closest approach of the two bodies).]

See the JPL Small-Body Database Browser on 3208 Lunn. The asteroid’s Earth MOID (Minimum Orbit Intersection Distance) is 1.808 AU, and its T_jup (Jupiter Tisserand invariant) is 3.206. [This is a measure of the orbital motion of an asteroid with respect to Jupiter, taking into account the semimajor axis, eccentricity, and inclination of the small body’s orbit, and remains broadly constant during the small body’s lifetime; it is named after the French astronomer François Félix Tisserand (1845–96).]

3208 Lunn: Designations and Name

Minor Planet Center: 3208 – Alternative Names: 1981 JM, 1931 GH, 1942 EA1, 1962 WN1

3208 Lunn was named in memory of Borge Lunn (1912 – 1986), a Danish civil engineer and metallurgist who did much to encourage the study of metal and iron meteorites. He invented a particular unmagnetized bronze for detailed experiments on the marine Galathea expedition in 1950, and for his work on the metallurgy of sleeve bearing metals he was awarded the Hunt Medal of the American Society of Lubrication Engineers. Twice chairman of the Danish Metallurgical Society, he served as head of the department of metallurgy at the Technical University of Denmark and was permanent censor in metallurgy in that department for 27 years.

Name proposed by the discoverer, following a suggestion of American planetary scientist Jonathan C. Gradie (who, in turn has asteroid 3253 named after him, also discovered at Anderson Mesa by Bowell).

3208 Lunn: Physical Characteristics

Absolute magnitude (H): 12.0 (Reference: PDS3 (MPC 28109) [The absolute magnitude (H) is the apparent magnitude that the object would have if it were one astronomical unit (AU) from both the Sun and the observer.]

Conversion of H to a diameter for a specific object requires knowledge of the object’s albedo. This quantity is not known for most objects including asteroid 3208 Lunn, so the diameters here are given as ranges. Most main-belt minor planets (of which 3208 Lunn is one) have albedos in the range 0.05 to 0.25. If a specific object has an albedo less than 0.05, the diameter will be larger than the upper limit listed here. For a rocky body, H = 12.0 corresponds to a probable diameter range of 11 to 24 km; for an icy body, the corresponding probable diameter range is 7 to 17 km.

3208 Lunn: Orbit Determination Parameters

Number of observations (all types) used in fit: 1269 – Number of days spanned by the data-arc: 29,982 days (82.09 years) – Date of first observation used in the fit: 1931-04-08 – Date of last observation used in the fit: 2013-05-09
JPL planetary ephemeris used in the orbit determination: DE431 – JPL small-body perturber ephemeris used in the orbit determination: SB431-BIG16
Minor Planet Center “U” parameter (orbit uncertainty estimate 0-9, with 0 = good and 9 = highly uncertain): 0 – Normalized RMS (Root Mean Square) of the fit: 0.5085
Data source: ORB – Name of person (or institution) who computed the orbit: Otto Matic – Date of orbit determination: 2013-Aug-05 14:26:03

Close Approaches to Jupiter

Data sorted by Date/Time (TDB). Reference: DISCOVERY.DB, Last Updated: 2003-08-29

Date/Time (date HH:MM) – Nominal Distance (AU)     

1929-07-15 16:51 – 1.90445984900976
1939-08-10 18:54 – 1.52042152306086
1949-09-03 14:31 – 1.77865380488157
2011-07-14 04:16 – 1.60831782240326
2021-08-04 08:33 – 1.60703121327334
2083-06-16 18:15 – 1.78071914067193
2093-07-06 22:19 – 1.5175749679223 
2103-08-04 13:33 – 1.91285637388741
2155-05-12 10:13 – 1.98055580422426
2175-07-02 07:26 – 1.71540172114789

3208 Lunn: The Supplemental IRAS Minor Planet Survey (SIMPS)

Authors: Tedesco E.F., Noah P.V., Noah M., Price S.D. – SIMPS Missed-Predictions File (Summary of the always-missed asteroids, i.e., those asteroids which were predicted to have crossed the IRAS focal plane array but which were never detected). – Information from file: datafileFP206.txt

Asteroid number and name or principal provisional designation: 3208 Lunn – Number of times predicted to be scanned but missed: 5 – Absolute magnitude on the H, G system: 12.00 – Slope parameter, G, on the H, G band system: 0.150 – Estimated visual geometric albedo: 0.0400 – Greatest lower bound on estimated visual geometric albedo: 0.0189 – Estimated diameter: 50.50 km – Least upper bound on the diameter: 38.50 km

[Most of this information is from the JPL Small-Body Database Browser and Wikipedia]

Spacecraft that have Visited Asteroids

Dawn (NASA Spacecraft),
Asteroid (4) Vesta and Dwarf Planet Ceres


Artist’s impression of Dawn with Vesta, Ceres and the Milky Way

Vesta by Dawn

Dawn (2007-043A), launched on 27th September 2007, successfully flew by Mars on 17th February 2009 on a gravity assist operation. After flying past Mars, Dawn crept up on asteroid (4) Vesta on 16th July 2011, becoming the first orbiter of a main-belt asteroid. It orbited asteroid (4) Vesta until 5th September 2012. After surveying the asteroid from many altitudes, Dawn departed from Vesta in the summer of 2012, embarking on a journey to end with orbit insertion at the dwarf planet Ceres in February 2015; the mission has been extended until 2016.

NEAR–Shoemaker (NASA spacecraft) and
Asteroids 253 Mathilde and 433 Eros

NEAR Shoemaker
NEAR Shoemaker

Near Earth Asteroid Rendezvous (NEAR) Shoemaker (1996-008A) was launched on 17th February 1996. The probe made a fly-by of Earth en route to asteroid 253 Mathilde. It successfully flew within 1200 km of Mathilde on 27th June 1997. On 23rd January 1998 it flew by the Earth for a gravity assist, making a closest approach of 540 km. Then on towards asteroid 433 Eros.


Asteroid 253 Mathilde

The first of four scheduled rendezvous burns was attempted on 20th December 1998 at 22:00 UTC. The burn sequence was initiated but immediately aborted; the spacecraft entered safe mode and began tumbling. The thrusters fired thousands of times during the anomaly, expending 29 kg of propellant reducing the propellant margin to zero; this anomaly almost resulted in the loss of the spacecraft due to lack of solar orientation and subsequent battery drain; contact between the spacecraft and mission control could not be established for over 24 hours. The original plan called for four burns to be followed by an orbit insertion burn on 10th January 1999, but this was impossible.

After the failure of the thrusters a new plan was put into effect in which NEAR flew by Eros on 23rd December 1998 at 18:41:23 UTC at a speed of 965 m/s and a distance of 3,827 km from the centre of mass of Eros; images were taken, data were collected by the near-infra-red spectrograph, and radio tracking was performed during the fly-by; a rendezvous manoeuvre on 3rd January 1999 involved a thruster burn to match NEAR’s orbital speed to that of Eros. A hydrazine thruster burn took place on 20th January 1999 to fine-tune the trajectory. On 12th August 1999 a two-minute thruster burn slowed the spacecraft velocity relative to Eros to 300 km/h.


Asteroid 433 Eros

This is a composite image of the north polar region of Eros, with the craters Psyche above and Himeros below. The long ridge Hinks Dorsum, believed to be a thrust fault, can be seen snaking diagonally between them. The smaller crater in the foreground is Narcissus.

High-resolution surface images and measurements made by NEAR’s Laser Rangefinder (NLR) have been combined into the above visualization based on the derived 3D model of the tumbling space rock. NEAR allowed scientists to discover that Eros is a single solid body, that its composition is nearly uniform, and that it formed during the early years of our Solar System. Mysteries remain, however, including why some rocks on the surface have disintegrated.

A rendezvous manoeuvre was completed on 3rd February 2000 at 17:00 UTC, slowing the spacecraft from 19.3 to 8.1 m/s relative to Eros; another manoeuvre on 8th February 2000 increased the relative velocity slightly to 9.9 m/s. Searches for satellites of Eros took place on 28th January, and 4th and 9th February 2000; none were found; the scans were for scientific purposes and to mitigate any chances of collision with a satellite. NEAR went into a 321×366 km elliptical orbit around Eros on 14th February 2000 after NEAR had completed a 13-month heliocentric orbit which closely matched that of Eros; it was slowly decreased to a 35 km circular polar orbit by 14th July 2000; NEAR remained in this orbit for 10 days and then was backed out in stages to a 100 km circular orbit by 5th September 2000. Manoeuvres in mid-October led to a fly-by of Eros within 5.3 km of the surface at 07:00 UTC on 26th October 2000. From 14th February 2000 to February 2001 the probe was close to Eros and went into orbit.

Following the fly-by NEAR moved to a 200 km circular orbit and shifted the orbit from prograde near-polar to a retrograde near-equatorial orbit; by 13th December 2000 the orbit was shifted back to a circular 35 km low orbit; starting on 24th January 2001 the spacecraft began a series of close passes (5 to 6 km) to the surface and on 28th January passed 2 to 3 km from the asteroid; in total NEAR made 230 orbits of Eros. With its fuel and funding nearly depleted, mission planners tried the unprecedented maneouvre of landing the orbiter on Eros. With fragile solar panels and protruding antennae, NEAR was never intended to be a lander. However, controllers successfully brought the spacecraft to a gentle 1.9 m/sec touchdown onto the rocky surface, taking 69 images during the final descent. The spacecraft then made a slow controlled descent to the surface of Eros ending with a touchdown just to the south of the saddle-shaped feature Himeros on 12th February 2001 at approximately 20:01 UTC. The spacecraft continued to function even after it landed.

The mission officially ended on 28th February 2001. At 7 p.m. EST the last data signals were received from NEAR Shoemaker before it was shut down. A final attempt to communicate with the spacecraft on 10th December 2002 was unsuccessful. This was probably due to the extreme (−173°C) conditions the probe experienced while on Eros. NEAR is likely to remain on the asteroid for billions of years as a monument to human ingenuity at the turn of the third millennium.

These four pictures are among the last ones taken by NEAR Shoemaker on 12th February 2001 near the end of its successful descent to the surface of Eros.

Eros from NEAR at 3773 ft
At about 1,150 m from the surface, showing an area about 54 m wide. The large boulder rests upon the surface with some overhang, while some of the smaller boulders appear partly buried by finer loose material

Eros from NEAR at 2300 ft
From a range of 700 m, showing an area 33 m across. Small craters and cracks are visible in individual boulders. Some of the boulders may be ejecta from distant craters, possibly broken apart further upon reimpact with the surface

Eros from NEAR at 820 ft
From a range of 250 m this shows an area only 12 m across. Different amounts of burial of the rocks and boulders are evident

Eros from NEAR at 394 ft
The last picture taken before touchdown from a range of 120 m, it measures 6 m across. The bottom of the picture was lost due to interruption of its transmission to Earth as the spacecraft touched down. Part of a large boulder is visible at the top. At the bottom is an area of very smooth material that shows sinous patterns of erosion

Hayabusa-1 (and “MINERVA”) and Hayabusa-2 (Japanese spacecraft) and Asteroids 25143 Itokawa and (162173) 1999 JU3

Hayabusa over Itokawa
A computer rendering of Hayabusa-1 above Itokawa

Hayabusa-1 (2003-019A), also called MUSES-C, was launched on 9th May 2003 and flew by the Earth again on 19th May 2004. It landed on asteroid 25143 Itokawa (1998 SF36) in September 2005 to 2007 and returned to Earth with samples on 13th June 2010. Its hopper, MINERVA (2003-019) missed its target on 12th November 2005.


Hayabusa 1

Hayabusa’s mission to and from asteroid Itokawa was one of the most thrilling adventures in modern space exploration, marked by numerous near-mission-ending disasters saved by the ingenuity of mission engineers, and culminating in the fiery death of the parent spacecraft on the night of the return of its sample capsule – a story much too long for this space (and dramatic enough to be the subject of three feature-length films in Japan). Hayabusa rendezvoused with and touched down on a very small asteroid. It successfully dropped a target marker containing 880,000 names to the surface, and then followed the marker down for two landing attempts. Upon the successful return of the sample capsule, a very small amount of asteroid dust was found inside, plenty for analysis by labs trained on the Stardust samples.


Japanese Spacecraft “Hayabusa” Re-entering the Atmosphere after Visiting Asteroid (25143) Itokawa


Hayabusa spacecraft during re-entry

The Hayabusa spacecraft was photographed over Southern Australia during its re-entry on 13th June 2010. It was launched in 2003 on a mission to visit the asteroid 25143 Itokawa and reached its destination in 2005, touching down and then returning to Earth with precious samples of asteroid dust.

Glowing with the heat of re-entry, the capsule sped across the sky from right to left, its colour and brightness changing as it passed through different layers of the atmosphere. The spacecraft also carried a detachable minilander, MINERVA, which failed to reach the surface.

Hayabusa-2 (Japanese Spacecraft)

After delays due to bad weather, Japan finally launched its Hayabusa-2 spacecraft (2014-76A) carrying a probe towards the asteroid (162173) 1999 JU3 on 3rd December 2014. The H-IIA rocket blasted off from Tanegashima Space Center at 0422 UTC.Malay Mail Online has a video of the launch and more about the mission.


Artist’s concept of the Hayabusa 2 spacecraft [JAXA/Akihiro Ikeshita]

The 31-billion-yen (200-million-euro) project will send the explorer on a six-year mission, and is expected to reach the asteroid in mid-2018 and spend around 18 months in the area. It will blast a crater in the asteroid to collect materials unexposed to millennia of wind and radiation, in the hope of answering some fundamental questions about life and the universe. It will also study the surface by dropping tiny robots. If all goes well, asteroid samples will be returned to Earth in late 2020 – AFP

Japanese officials say the probe has passed health checks and is ready for the long-distance journey ahead. “The Hayabusa 2 spacecraft “completed its initial functional confirmation period on 2nd March 2015, as all scheduled checkout and evaluation of acquired data were completed”, the Japan Aerospace Exploration Agency said in a statement. “The explorer has been under inspection for about three months after its launch”.

The probe carries four ion thrusters to nudge it on course toward asteroid 1999 JU3, a carbon-rich world just 900 metres across with a tenuous gravity field 60,000 times weaker than Earth’s. The engines produce little thrust, but the units can be operated for thousands of hours, building up energy to reshape Hayabusa 2’s path around the sun. JAXA says two of the ion engines will fire for about 400 hours in March to give the spacecraft a boost. Two thrusters will be operated again in early June. The two periods of near-continuous propulsion will change the probe’s velocity by about 60 metres per second to align Hayabusa 2 with an encounter with Earth in December. The close flyby of Earth will use the planet’s gravity to slingshot Hayabusa 2 toward its destination, where it is due to arrive in June 2018 after more firings of the craft’s ion engines.

Since Hayabusa 2’s launch, ground controllers tested the probe’s X-band and Ka-band communications systems, batteries, science instruments, reaction wheels, and all four ion engines. Hayabusa 2 also extended its sampling device in preparation for scooping up material at the asteroid. Engineers tested Hayabusa 2’s German-built lander named MASCOT built by the same team that managed the Philae comet lander, which was carried aboard Europe’s Rosetta spacecraft and touched down on comet 67P/Churyumov–Gerasimenko in November 2014. Three other landing craft built in Japan will also descend to the asteroid during Hayabusa 2’s mission. The landers are mobile and will use mechanisms to hop across the asteroid to study its environment from several locations.

Hayabusa 2 will spend a 1½ years at asteroid 1999 JU3, enough time for the probe to pick up rock specimens from three different locations on the unexplored asteroid. Once the mission’s work at the asteroid is complete, Hayabusa 2 will leave and head for Earth in December 2019. Hayabusa 2 will release a container with the asteroid samples for a blazing re-entry through Earth’s atmosphere with a parachute-assisted landing in the Australian outback in December 2020.

Deep Space 1


Deep Space 1 encounters asteroid 9969 Braille

Deep Space 1 visited asteroid 9969 Braille [artist’s impression] and went on to Comet 19P/Borelly. The craft was launched from Cape Canaveral by a Delta rocket on 24th October 1998 [COSPAR ID 1998-061A]. Its primary mission was to test new technology for future interplanetary spacecraft, the main experiment being an ion propulsion engine using xenon propellant. Deep Space 1 successfully started its ion engine on 24th November after an initial attempt failed after four minutes on 10th November. From its initial solar orbit, Deep Space 1 flew past the 3 km diameter asteroid 9969 Braille (1992 KD) on 29th July 1999 at its perihelion of 1.33 AU. The spacecraft then flew past the nucleus of comet 19P/Borrelly at a distance of 2200 km at 2230 GMT on 22nd September 2001. It survived the encounter in good shape, sending back photos of the comet.

Clementine (NASA spacecraft) and Asteroid 1620 Geographos

Clementine (1994-004A) (officially called the Deep Space Program Science Experiment (DSPSE)) was a joint space project between the Ballistic Missile Defense Organization (BMDO, previously the Strategic Defense Initiative Organization, or SDIO) and NASA. It was launched on 25th January 1994 at 16:34:00 UTC, the objective of the mission, to test sensors and spacecraft components under extended exposure to the space environment and to make scientific observations of the Moon and the near-Earth asteroid 1620 Geographos.

Clementine
A three-dimensional model of 1620 Geographos that was computed using light curve inversion techniques

Technicians checking Clementine before its launch

Clementine attemped a flyby of asteroid 1620 Geographos in 1994 but the flyby was cancelled due to an equipment malfunction. Its instruments were a charged particle telescope (to measure the flux and spectra of energetic protons and electrons; an ultraviolet/visible camera (to study the Moon and 1620 Geographos at five different wavelengths in the ultraviolet spectrum; a near-Infrared CCD camera (NIR) (to study the Moon and 1620 Geographos at six different wavelengths in the near-infrared spectrum; a laser Image Detection and Ranging (LIDAR) system (to measure the distance from the spacecraft to a point on the surface of the Moon); a high-resolution camera (HIRES) (to study selected portions of the Moon and asteroid).

The mission ended in June 1994 when the power level onboard dropped to a point where the telemetry from the spacecraft was no longer intelligible. NASA announced on 5th March 1998 that data obtained from Clementine indicated that there is enough water in polar craters of the moon to support a human colony and a rocket fueling station. Doubt has since been cast on this interpretation, however. See also Clementine and the moon.