User:Marshallsumter/Rocks/Rocky objects/Asteroids

Asteroids are small rocky, metallic or icy objects that orbit the Sun or another star.

Large numbers of asteroids as indicated in the image from Gaia at the top ranging in size from Ceres to dust particles are found in the asteroid belt especially between the orbits of Mars and Jupiter.

1999 JU3
"Asteroid 1999 JU3 is a so-called carbonaceous, or C-type, space rock — a different type of asteroid than the rocky (S-type) asteroid Itokawa visited by the first Hayabusa. Scientists suspect asteroid 1999 JU3 holds water and organic materials — some of the building blocks of the solar system."

2007 VK184
"Recent observations have removed from NASA's asteroid impact hazard list the near-Earth object (NEO) known to pose the most significant risk of Earth impact over the next 100 years."

"2007 VK184, an asteroid estimated to be roughly 130 meters in size, has been on NASA's Impact Risk Page maintained by the NEO Program Office at the Jet Propulsion Laboratory (JPL) for several years, with an estimated 1-in-1800 chance of impacting Earth in June 2048. This predicted risk translates to a rating of 1 on the 10-point Torino Impact Hazard Scale. In recent months, 2007 VK184 has been the only known NEO with a non-zero Torino Scale rating."

"2007 VK184 was discovered in November 2007 by the NASA-funded Catalina Sky Survey (CSS) at the University of Arizona and tracked by the CSS and other stations for two months before moving beyond view of ground based telescopes in January 2008."

"But in the early morning hours of March 26 and 27, 2014, Dr. David Tholen of the University of Hawaii sighted 2007 VK184 once again. Using the 3.6-meter-diameter Canada-France-Hawaii Telescope at the Mauna Kea Observatories in Hawaii, he was able to detect and track the asteroid. Because it had not been observed for almost six years, its predicted position was only approximate. Nonetheless, Dr. Tholen was able to find it within the predicted search region, which is called a "recovery." He measured the asteroid's position and movement relative to the background of stars, and forwarded his tracking data to the Minor Planet Center (MPC) in Cambridge, Massachusetts, the central node for the global NEO observer community."

"Although the asteroid will be closer to Earth and brighter in May, I made the recovery attempt in March because I didn't want the position uncertainty to grow so much that it would force a time-consuming search of much more of the sky. The trade-off was increased exposure time to detect such a faint, distant object. Greater atmospheric turbulence on March 26 blurred the images of the asteroid enough to make the detection questionable, but the March 27 images were much better and confirmed the recovery."

"The "Sentry" asteroid monitoring system at JPL automatically retrieved the new observations of 2007 VK184 from the MPC database, updated the orbit for the object, and computed a new impact hazard assessment. This new work shows that 2007 VK184 will pass no closer than 1.9 million kilometers (1.2 million miles) from the Earth in June 2048, with no closer encounters predicted for the foreseeable future. The NEO Program Office removed 2007 VK184 from the Impact Risk Page about three hours after receiving Dr. Tholen's observations from the MPC."

"While these new observations of 2007 VK184 were challenging for Dave Tholen to obtain, they were reported quickly, and the global, distributed NEO impact hazard monitoring system worked smoothly to provide the all-clear for this object."

"JPL's Sentry is an automated monitoring system that continually scans the most current catalog of known asteroids and predicts potential hazards of impacts with Earth over the next 100 years. As additional observations become available, objects will be removed from Sentry's Impact Risk Page when sufficient data become available to eliminate any potential for impact in the projected future. According to the Torino Impact Hazard Scale, developed and used by NEO observers to assess potential impact risks, a rating of 1 indicates a predicted event that "merits careful monitoring," and a rating of zero indicates the predicted event has "no likely consequences.""

"Objects typically appear on the Sentry Impact Risk Page because a limited number of available observations may indicate a potential hazard of impact with Earth but do not provide astronomers enough information to precisely define their orbital movements. Whenever a newly discovered NEO is posted on the Sentry Impact Risk Page, the most likely outcome is that the object will eventually be removed as new observations become available, the object's orbit is more precisely known, and its future motion is more tightly constrained. NASA's NEO Program Office at JPL, which operates Sentry, receives asteroid observations and orbit predictions daily from the MPC. Once an asteroid is classified as a near-Earth object, the Sentry system automatically calculates orbit updates for it as new data become available."

"NASA's Near-Earth Object Observation (NEOO) Program, located in the Planetary Science Division of the Science Mission Directorate at NASA Headquarters in Washington, D.C., is responsible for finding, tracking, and characterizing near-Earth objects (NEOs) - asteroids and comets whose orbits periodically bring them close to Earth. The NEOO Program sponsors internal NASA and external research projects. The Jet Propulsion Laboratory (JPL) in Pasadena, California, manages a NEO Program Office for the Headquarters' NEOO Program and conducts a number of NASA-sponsored NEO projects."

"Asteroid 2007 VK184 is another case study on how our system works."

"We find them, track them, learn as much as we can about those found to be of special interest - an impact hazard or a space mission destination - and we predict and monitor their movement in the inner solar system until we know they are of no more concern."

2012 LZ1
The image at right is of asteroid 2012 LZ1 using the Arecibo Planetary Radar.

"On Sunday, June 10, a potentially hazardous asteroid thought to have been 500 meters (0.31 miles) wide was discovered by Siding Spring Observatory in New South Wales, Australia. Fortunately for us, asteroid 2012 LZ1 drifted safely by, coming within 14 lunar distances from Earth on Thursday, June 14."

"Asteroid 2012 LZ1 is actually bigger than thought… in fact, it is quite a lot bigger. 2012 LZ1 is one kilometer wide (0.62 miles), double the initial estimate."

Asteroid "2012 LZ1′s surface is really dark, reflecting only 2-4 percent of the light that hits it — this contributed to the underestimated initial optical observations. Looking for an asteroid the shade of charcoal isn’t easy."

“This object turned out to be quite a bit bigger than we expected, which shows how important radar observations can be, because we’re still learning a lot about the population of asteroids”.

“The sensitivity of our radar has permitted us to measure this asteroid’s properties and determine that it will not impact the Earth at least in the next 750 years”.

1 Ceres
High-resolution ultraviolet Hubble Space Telescope images taken in 1995 showed a dark spot on its surface which was nicknamed "Piazzi" in honour of the discoverer of Ceres. This was thought to be a crater. Later near-infrared images with a higher resolution taken over a whole rotation with the Keck telescope using adaptive optics showed several bright and dark features moving with the dwarf planet's rotation.

"This pair of images shows color-coded maps from NASA's Dawn mission, revealing the highs and lows of topography on the surface of dwarf planet Ceres."

"The map at left is centered on terrain at 60 degrees east longitude; the map at right is centered on 240 degrees east longitude."

"The color scale extends about 5 miles (7.5 kilometers) below the surface in indigo to 5 miles (7.5 kilometers) above the surface in white."

"The topographic map was constructed from analyzing images from Dawn's framing camera taken from varying sun and viewing angles. The map was combined with an image mosaic of Ceres and projected as an orthographic projection."

"The well-known bright spots in the center of Ceres northern hemisphere in the image at right retain their bright appearance, although they are color-coded in the same green elevation of the crater floor in which they sit."

"Note: The elevation scale used for this topographic map product differs slightly from the scale used to create PIA19605."

2 Pallas
"Pallas, minor-planet designation 2 Pallas, is the second asteroid to have been discovered (after Ceres), and one of the largest in the Solar System. It is estimated to comprise 7% of the mass of the asteroid belt, and its diameter of 544 km is slightly larger than that of 4 Vesta. It is however 10–30% less massive than Vesta, placing it third among the asteroids.

3 Juno
3 Juno is a siliceous asteroid type S(IV).

4 Vesta
"The [NASA's Dawn spacecraft] Framing Camera (FC) discovered enigmatic orange material on Vesta. FC images revealed diffuse orange ejecta around two impact craters, 34-km diameter Oppis, and 30-km diameter Octavia, as well as numerous sharp-edge orange units in the equatorial region." The spacecraft "entered orbit around asteroid (4) Vesta in July 2011 for a year-long mapping orbit."

"Using Dawn’s Gamma Ray and Neutron Detector, ... Global Fe/O and Fe/Si ratios are consistent with [howardite, eucrite, and diogenite] HED [meteorite] compositions."

"To prepare for the Dawn spacecraft's visit to Vesta, astronomers used Hubble's Wide Field Planetary Camera 2 to snap new images of the asteroid. The image at right was taken on May 14 and 16, 2007. Using Hubble, astronomers mapped Vesta's southern hemisphere, a region dominated by a giant impact crater formed by a collision billions of years ago. The crater is 285 miles (456 kilometers) across, which is nearly equal to Vesta's 330-mile (530-kilometer) diameter. If Earth had a crater of proportional size, it would fill the Pacific Ocean basin. The impact broke off chunks of rock, producing more than 50 smaller asteroids that astronomers have nicknamed "vestoids." The collision also may have blasted through Vesta's crust. Vesta is about the size of Arizona."

"Previous Hubble images of Vesta's southern hemisphere were taken in 1994 and 1996 with the wide-field camera. In this new set of images, Hubble's sharp "eye" can see features as small as about 37 miles (60 kilometers) across. The image shows the difference in brightness and color on the asteroid's surface. These characteristics hint at the large-scale features that the Dawn spacecraft [sees] when it arrives at Vesta."

"Hubble's view reveals extensive global features stretching longitudinally from the northern hemisphere to the southern hemisphere. The image also shows widespread differences in brightness in the east and west, which probably reflects compositional changes. Both of these characteristics could reveal volcanic activity throughout Vesta. The size of these different regions varies. Some are hundreds of miles across."

"The brightness differences could be similar to the effect seen on the Moon, where smooth, dark regions are more iron-rich than the brighter highlands that contain minerals richer in calcium and aluminum. When Vesta was forming 4.5 billion years ago, it was heated to the melting temperatures of rock. This heating allowed heavier material to sink to Vesta's center and lighter minerals to rise to the surface."

"Astronomers combined images of Vesta in two colors to study the variations in iron-bearing minerals. From these minerals, they hope to learn more about Vesta's surface structure and composition."

"The simplest model for the genesis of the HED meteorites involves a series of partial melting and crystallization events [1] of a small parent body whose bulk composition is more or less consistent with cosmic abundances but is depleted in the moderately volatile elements Na and K [2]."

"Why should both Vesta and the Moon be rich in oxidized Fe but depleted in Na and K?"

"How did the HEDs get here from Vesta? The discovery of a string of Vesta-like asteroids in orbits linking Vesta to nearby orbital resonances [5] has shown that [...] arguments [...] for material originating at Vesta to reach Earth-crossing orbits are [...] valid."

"An alternative theory is based on electromagnetic heating during an episode of strong solar wind from the early proto-Sun when our star experienced a T Tauri phase, as predicted by modern stellar astrophysics."

6 Hebe
6 Hebe is a siliceous asteroid of subtype IV [S(IV)].

The image on the right is a photograph of 6 Hebe (the brightest spot) in 2004.

"Compositional analysis of 2007 LE reveal Fs17 and Fa19 values, which are consistent with the Fa and Fs values for the H-type ordinary chondrites (Fs14.5–18 and Fa16–20) and of Asteroid (6) Hebe (Fs17 and Fa15)."

"It is probable that the H-chondrites and IIE irons came from (6) Hebe (Gaffey and Gilbert, 1998), though caveats exist (e.g., Rubin and Bottke, 2009)."

8 Flora
8 Flora may be ambiguously a type S(II-III) siliceous asteroid.

9 Metis
9 Metis is a siliceous asteroid.

11 Parthenope
11 Parthenope is a siliceous asteroid type S(IV).

12 Victoria
12 Victoria is a siliceous asteroid of subtype II [S(II)].

15 Eunomia
15 Eunomia is a siliceous asteroid of subtype III [S(III)].

16 Psyche
A "huge, metallic asteroid named 16 Psyche [...] resides" in the asteroid belt.

16 Psyche is "a 130-mile-wide (210 kilometers) metallic asteroid that may be the core of an ancient, Mars-size planet. Violent collisions billions of years ago might have stripped away the layers of rock that once lay atop this metallic object."

"16 Psyche is the only known object of its kind in the solar system, and this is the only way humans will ever visit a core. We learn about inner space by visiting outer space."

The "asteroid Psyche displays significant variations in radar and optical albedo with rotation."

"16 Psyche [is] the largest M-class asteroid in the main belt."

"18 radar imaging and 6 continuous wave runs in November and December 2015, [were] combined [...] with 16 continuous wave runs from 2005 and 6 recent adaptive-optics (AO) images (Drummond et al., 2016) to generate a three-dimensional shape model of Psyche."

The "shape model has dimensions 279 × 232 × 189 km (± 10%), Deff = 226 ± 23 km, and is 6% larger than, but within the uncertainties of, the most recently published size and shape model generated from the inversion of lightcurves (Hanus et al., 2013). Psyche is roughly ellipsoidal but displays a mass-deficit over a region spanning 90° of longitude. There is also evidence for two ∼50–70 km wide depressions near its south pole. Their size and published masses lead to an overall bulk density estimate of 4500 ± 1400 kg·m−3. Psyche's mean radar albedo of 0.37 ± 0.09 is consistent with a near-surface regolith composed largely of iron-nickel and ∼40% porosity. Its radar reflectivity varies by a factor of 1.6 as the asteroid rotates, suggesting global variations in metal abundance or bulk density in the near surface."

18 Melpomene
18 Melpomene is a siliceous asteroid type S(V).

20 Massalia
20 Massalia is a siliceous asteroid type S(VI).

25 Phocaea
25 Phocaea is a siliceous asteroid type S(IV).

26 Proserpina
26 Proserpina is a siliceous asteroid of subtype II [S(II)].

27 Euterpe
27 Euterpe is a siliceous asteroid type S(IV).

29 Amphitrite
29 Amphitrite is a siliceous asteroid type S(V).

33 Polyhymnia
33 Polyhymnia is a siliceous asteroid type S(IV).

37 Fides
37 Fides is a siliceous asteroid type S(V).

39 Laetitia
39 Laetitia is a siliceous asteroid of subtype II [S(II)].

42 Isis
42 Isis is a siliceous asteroid of subtype I [S(I)].

43 Ariadne
43 Ariadne is a siliceous asteroid of subtype III [S(III)].

57 Mnemosyne
57 Mnemosyne is a siliceous asteroid type S(VII).

63 Ausonia
63 Ausonia is a siliceous asteroid of subtype III [S(III)].

"Ausonia is classed ambiguously as type S(II-III)."

67 Asia
67 Asia is a siliceous asteroid type S(IV).

68 Leto
68 Leto is a siliceous asteroid of subtype II [S(II)].

80 Sappho
80 Sappho is a siliceous asteroid type S(IV).

82 Alkmene
82 Alkmene is a siliceous asteroid type S(VI).

89 Julia
89 Julia is a siliceous asteroid.

101 Helena
101 Helena is a siliceous asteroid type S(V).

113 Amalthea
113 Amalthea is a siliceous asteroid of subtype I [S(I)].

115 Thyra
115 Thyra is a siliceous asteroid of subtype III [S(III)].

197 Arete
"More than 150 years after the discovery of 4 Vesta in 1807, Hertz (1966) made the first asteroid mass determination by analyzing its perturbation on 197 Arete."

243 Ida
"This is the first full picture [on the right] showing both asteroid 243 Ida and its newly discovered moon to be transmitted to Earth from the National Aeronautics and Space Administration's (NASA's) Galileo spacecraft--the first conclusive evidence that natural satellites of asteroids exist. Ida, the large object, is about 56 kilometers (35 miles) long. Ida's natural satellite is the small object to the right. This portrait was taken by Galileo's charge-coupled device (CCD) camera on August 28, 1993, about 14 minutes before the Jupiter-bound spacecraft's closest approach to the asteroid, from a range of 10,870 kilometers (6,755 miles). Ida is a heavily cratered, irregularly shaped asteroid in the main asteroid belt between Mars and Jupiter--the 243rd asteroid to be discovered since the first was found at the beginning of the 19th century. Ida is a member of a group of asteroids called the Koronis family. The small satellite, which is about 1.5 kilometers (1 mile) across in this view, has yet to be given a name by astronomers. It has been provisionally designated '1993 (243) 1' by the International Astronomical Union. ('1993' denotes the year the picture was taken, '243' the asteroid number and '1' the fact that it is the first moon of Ida to be found.) Although appearing to be 'next' to Ida, the satellite is actually in the foreground, slightly closer to the spacecraft than Ida is. Combining this image with data from Galileo's near-infrared mapping spectrometer, the science team estimates that the satellite is about 100 kilometers (60 miles) away from the center of Ida. This image, which was taken through a green filter, is one of a six-frame series using different color filters. The spatial resolution in this image is about 100 meters (330 feet) per pixel."

On the second lower right is an approximately natural color image of the asteroid 243 Ida. "There are brighter areas, appearing bluish in the picture, around craters on the upper left end of Ida, around the small bright crater near the center of the asteroid, and near the upper right-hand edge (the limb). This is a combination of more reflected blue light and greater absorption of near infrared light, suggesting a difference in the abundance or composition of iron-bearing minerals in these areas."

246 Asporina
246 Asporina is an A-type asteroid.

253 Mathilde
Mathide is a carbonaceous (C) asteroid.

"The masses of 253 Mathide (Yeomans et al., 1998) and Eros (Yeomans et al., 2000) are the first two asteroid masses determined by observing the perturbation of a spacecraft in the vicinity of the asteroid."

258 Tyche
258 Tyche is a siliceous asteroid type S(V).

264 Libussa
264 Libussa is a siliceous asteroid type S(V).

289 Nenetta
289 Nenetta is an A asteroid.

335 Roberta
335 Roberta is a blue asteroid.

354 Eleonora
354 Eleonora is a siliceous asteroid of subtype I [S(I)].

364 Isara
364 Isara is a siliceous asteroid of subtype II [S(II)].

389 Industria
389 Industria is a siliceous asteroid type S(V).

433 Eros
"In 2000, 433 Eros became the first asteroid to be orbited by a spacecraft, NEAR Shoemaker (Yeomans et al., 2000)."

446 Aeternitas
446 Aeternitas is an A asteroid.

532 Herculina
532 Herculina is a siliceous asteroid of subtype III [S(III)].

584 Semiramis
584 Semiramis is a siliceous asteroid type S(IV).

674 Rachele
674 Rachele is a siliceous asteroid of subtype VII [S(VII)].

951 Gaspra
The "Galileo flyby images of 951 Gaspra suggest the presence of some regolith on that 16- by 12-km object (e.g., Belton et al. 1992)."

1036 Ganymed
1036 Ganymed is a siliceous asteroid type S(VI-VII).

4179 Toutatis
At right is a Goldstone radar image of the asteroid 4179 Toutatis on November 26, 1996.

The "images were recorded at NASA's Deep Space Network 70-meter and 34-meter radio/radar antennas in Goldstone, CA, and the 305-meter Arecibo Radio Telescope in Puerto Rico." "It's amazing that the shape of Toutatis can be determined so accurately from ground-based observations".

"This technology will provide us with startling, close-up views of thousands of asteroids that orbit near the Earth."

"We used the computer to mathematically create a three- dimensional model of the surface and rotation of Toutatis".

"It's as though we put a clay model in space and molded it until it matched the appearance of the actual asteroid."

"The video is of particular interest as Toutatis nears Earth and makes its closest approach on Friday, Nov. 29, when it will pass by at a distance of 3.3 million miles (5.3 million kilometers), or about 14 times the distance from the Earth to the Moon. In 2004, Toutatis will pass only four lunar distances from Earth, closer than any known Earth- approaching object expected to pass by in the next 60 years."

"Toutatis poses no significant threat to Earth, at least for a few hundred years".

"The discovery that we live in an asteroid swarm is important for the future of humanity".

"These leftover debris from planetary formation can teach us a good deal about the formation of our Solar System. Asteroids also contain valuable minerals and many are the cheapest possible destinations for space missions."

On September 29, 2004 the asteroid 4179 Toutatis made a particularly close approach (within 4 LD, or lunar distances) from Earth. The next close approach is November 9, 2008, but it will be five times more distant. It is about 4.6 km by 2.4 km in size.

99942 Apophis
There is some concern that the asteroid 99942 Apophis could impact Earth on April 13, 2036. It is about 210 - 330 meters in size. The probability of a collision is currently esitmated to be 1 in 45,000. These calculations are uncertain due to another close encounter in 2029 which will modify the orbit of the asteroid, making a collision either more or less likely. New measurements possible in 2011-2013 will likely confirm that the asteroid will miss the Earth.

Hypotheses

 * 1) Asteroids are any-size rocky astronomical objects.