Estimation of average rock and asteroid mass associated with different stars

Estimation of average rock and asteroid mass associated with different stars

There is a lot of information on different star types and compositions.

Can we make estimates of the total mass of rock, ice, and non stellar matter that orbits stars based on star evolution models?

Take, for example, the sun - are there studies of the total mass of non-solar material associated with the sun and it's composition regardless of accretion. What about nearby stars?

Can we estimate how much non-incandescent material the galaxy contains aside from dark matter?

The composition of the gas from which stars and their planetary systems form is reasonably well known. About 1-2% of this gas is in the form of chemical elements heavier than Helium (the so-called metallicity of the gas).

A fraction of these "metals" - the iron, silicon, oxygen etc. is capable of forming dust and then accumulating to form "rocky" material.

So to answer your last question first, given the available reservoir it seems most unlikely that even 1% of the baryonic (normal) matter in the universe could be rocks, even if none of it were gathered into luminous stars and galaxies.

Forming stars are surrounded by circumstellar material from which planets and other rocks form. Observations of young stars suggest these discs can be as massive as 10% of the stellar mass, but more usually 1% or less. This means that as a fraction of the whole formed star system the rocks will be at most 1% of 10% (ie 0.1%) of the stellar mass. For a Sun-like star that means there's less than 330 Earth masses of rocky material around it.

Estimation of average rock and asteroid mass associated with different stars - Astronomy

Dwarf planet Ceres is the largest object in the asteroid belt between Mars and Jupiter and the only dwarf planet located in the inner solar system. It was the first member of the asteroid belt to be discovered when Giuseppe Piazzi spotted it in 1801. And when Dawn arrived in 2015, Ceres became the first dwarf planet to receive a visit from a spacecraft.

Called an asteroid for many years, Ceres is so much bigger and so different from its rocky neighbors that scientists classified it as a dwarf planet in 2006. Even though Ceres comprises 25 percent of the asteroid belt's total mass, tiny Pluto is still 14 times more massive.

Ceres is named for the Roman goddess of corn and harvests. The word cereal comes from the same name. Explore Ceres &rsaquo


Early in the life of the solar system, dust and rock circling the sun were pulled together by gravity into planets. But not all of the ingredients created new worlds. A region between Mars and Jupiter became the asteroid belt.

Occasionally people wonder whether the belt was made up of the remains of a destroyed planet, or a world that didn't quite get started. However, according to NASA, the total mass of the belt is less than the moon, far too small to weigh in as a planet. Instead, the debris is shepherded by Jupiter, which kept it from coalescing onto other growing planets.

Observations of other planets are helping scientists to better understand the solar system. According to a developing theory known as Grand Tack, in the first 5 million years of the solar system, Jupiter and Saturn are thought to have moved inward toward the sun before changing direction and heading back to the outer solar system. Along the way, they would have scattered the original asteroid belt before them, then sent material flying back to refill it.

"In the Grand Tack model, the asteroid belt was purged at a very early stage and the surviving members sample a much larger region of the solar nebula," John Chambers of the Carnegie Institution for Science wrote in a "Perspectives" piece published online in the journal Science.

Our solar system isn't the only one to boast an asteroid belt. A cloud of dust around a star known as zeta Leporis looks a lot like a young belt. "Zeta Leporis is a relatively young star — approximately the age of our sun when the Earth was forming," Michael Jura said in a statement. "The system we observed around zeta Leporis is similar to what we think occurred in the early years of our own solar system when planets and asteroids were created." A professor at the University of California, Los Angeles, Jura has since passed away.

Other stars also contain signs of asteroid belts, suggesting that may be common.

At the same time, studies of white dwarfs, sun-like stars at the end of their lifetimes, show signatures of rocky material falling onto their surface that suggest such belts are common around dying systems.

Physical characteristics of Vesta

Vesta is unique among asteroids in that it has light and dark patches on the surface, much like the moon. Ground-based observations determined that the asteroid has basaltic regions, meaning that lava once flowed across its surface. It has an irregular shape, roughly that of an oblate spheroid (in nontechnical terms, a somewhat smooshed sphere).

  • Diameter: 329 miles (530 kilometers)
  • Mass: 5.886 X 10 20 lbs. (2.67 x 10 20 kilograms)
  • Temperature: 85 to 255 K (minus 306 to 0 degrees Fahrenheit / minus 188 to minus 18 degrees Celsius)
  • Albedo: 0.4322
  • Rotation period: 5.342 hours
  • Orbital period: 3.63 years
  • Eccentricity: .0886
  • Aphelion: 2.57 AU
  • Perihelion: 2.15 AU
  • Closest approach to Earth: 1.14 AU

FAQ: What is a Meteor Shower?

Scientists estimate that about 48.5 tons (44 tonnes or 44,000 kilograms) of meteoritic material falls on the Earth each day. Almost all the material is vaporized in Earth's atmosphere, leaving a bright trail fondly called "shooting stars." Several meteors per hour can usually be seen on any given night. Sometimes the number increases dramatically&mdashthese events are termed meteor showers.

Meteor showers occur annually or at regular intervals as the Earth passes through the trail of dusty debris left by a comet. Meteor showers are usually named after a star or constellation that is close to where the meteors appear in the sky. Perhaps the most famous are the Perseids, which peak in August every year. Every Perseid meteor is a tiny piece of the comet Swift-Tuttle, which swings by the Sun every 135 years.

How to Photograph a Meteor Shower

For first time, astronomers catch asteroid in the act of changing color

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Last December, scientists discovered an “active” asteroid within the asteroid belt, sandwiched between the orbits of Mars and Jupiter. The space rock, designated by astronomers as 6478 Gault, appeared to be leaving two trails of dust in its wake — active behavior that is associated with comets but rarely seen in asteroids.

While astronomers are still puzzling over the cause of Gault’s comet-like activity, an MIT-led team now reports that it has caught the asteroid in the act of changing color, in the near-infrared spectrum, from red to blue. It is the first time scientists have observed a color-shifting asteroid, in real-time.

“That was a very big surprise,” says Michael Marsset, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “We think we have witnessed the asteroid losing its reddish dust to space, and we are seeing the asteroid’s underlying, fresh blue layers.”

Marsset and his colleagues have also confirmed that the asteroid is rocky — proof that the asteroid’s tail, though seemingly comet-like, is caused by an entirely different mechanism, as comets are not rocky but more like loose snowballs of ice and dust.

“It’s the first time to my knowledge that we see a rocky body emitting dust, a little bit like a comet,” Marsset says. “It means that probably some mechanism responsible for dust emission is different from comets, and different from most other active main-belt asteroids.”

Marsset and his colleagues, including EAPS Research Scientist Francesca DeMeo and Professor Richard Binzel, have published their results today in the journal Astrophysical Journal Letters.

A rock with tails

Astronomers first discovered 6478 Gault in 1988 and named the asteroid after planetary geologist Donald Gault. Until recently, the space rock was seen as relatively average, measuring about 2.5 miles wide and orbiting along with millions of other bits of rock and dust within the inner region of the asteroid belt, 214 million miles from the sun.

In January, images from various observatories, including NASA’s Hubble Space Telescope, captured two narrow, comet-like tails trailing the asteroid. Astronomers estimate that the longer tail stretches half a million miles out, while the shorter tail is about a quarter as long. The tails, they concluded, must consist of tens of millions of kilograms of dust, actively ejected by the asteroid, into space. But how? The question reignited interest in Gault, and studies since then have unearthed past instances of similar activity by the asteroid.

“We know of about a million bodies between Mars and Jupiter, and maybe about 20 that are active in the asteroid belt,” Marsset says. “So this is very rare.”

He and his colleagues joined the search for answers to Gault’s activity in March, when they secured observation time at NASA’s Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Over two nights, they observed the asteroid and used a high-precision spectrograph to divide the asteroid’s incoming light into various frequencies, or colors, the relative intensities of which can give scientists an idea of an object’s composition.

From their analysis, the team determined that the asteroid’s surface is composed mainly of silicate, a dry, rocky material, similar to most other asteroids, and, more importantly, not at all like most comets.

Comets typically come from the far colder edges of the solar system. When they approach the sun, any surface ice instantly sublimates, or vaporizes into gas, creating the comet’s characteristic tail. Since Marsset’s team has found 6478 Gault is a dry, rocky body, this means it likely is generating dust tails by some other active mechanism.

A fresh change

As the team observed the asteroid, they discovered, to their surprise, that the rock was changing color in the near-infrared, from red to blue.

“We've never seen such a dramatic change like this over such a short period of time,” says co-author DeMeo.

The scientists say they are likely seeing the asteroid’s surface dust, turned red over millions of years of exposure to the sun, being ejected into space, revealing a fresh, less irradiated surface beneath, that appears blue at near-infrared wavelengths.

“Interestingly, you only need a very thin layer to be removed to see a change in the spectrum,” DeMeo says. “It could be as thin as a single layer of grains just microns deep.”

So what could be causing the asteroid to turn color? The team and other groups studying 6478 Gault believe the reason for the color shift, and the asteroid’s comet-like activity, is likely due to the same mechanism: a fast spin. The asteroid may be spinning fast enough to whip off layers of dust from its surface, through sheer centrifugal force. The researchers estimate it would need to have about a two-hour rotation period, spinning around every couple of hours, versus Earth’s 24-hour period.

“About 10 percent of asteroids spin very fast, meaning with a two- to three-hour rotation period, and it’s most likely due to the sun spinning them up,” says Marsset.

This spinning phenomenon is known as the YORP effect (or, the Yarkovsky-O’Keefe-Radzievskii-Paddack effect, named after the scientists who discovered it), which refers to the effect of solar radiation, or photons, on small, nearby bodies such as asteroids. While asteroids reflect most of this radiation back into space, a fraction of these photons is absorbed, then reemitted as heat, and also momentum. This creates a small force that, over millions of years, can cause the asteroid to spin faster.

Astronomers have observed the YORP effect on a handful of asteroids in the past. To confirm a similar effect is acting on 6478 Gault, researchers will have to detect its spin through light curves — measurements of the asteroid’s brightness over time. The challenge will be to see through the asteroid’s considerable dust tail, which can obscure key portions of the asteroid’s light.

Marsset’s team, along with other groups, plan to study the asteroid for further clues to activity, when it next becomes visible in the sky.

“I think [the group’s study] reinforces the fact that the asteroid belt is a really dynamic place,” DeMeo says. “While the asteroid fields you see in the movies, all crashing into each other, is an exaggeration, there is definitely a lot happening out there every moment.”

This research was funded, in part, by the NASA Planetary Astronomy Program.


Discovery Edit

Heinrich Olbers discovered Pallas in 1802, the year after the discovery of Ceres. He proposed that the two objects were the remnants of a destroyed planet. He sent a letter with his proposal to the British astronomer William Herschel, suggesting that a search near the locations where the orbits of Ceres and Pallas intersected might reveal more fragments. These orbital intersections were located in the constellations of Cetus and Virgo. [34] Olbers commenced his search in 1802, and on 29 March 1807 he discovered Vesta in the constellation Virgo—a coincidence, because Ceres, Pallas, and Vesta are not fragments of a larger body. Because the asteroid Juno had been discovered in 1804, this made Vesta the fourth object to be identified in the region that is now known as the asteroid belt. The discovery was announced in a letter addressed to German astronomer Johann H. Schröter dated 31 March. [35] Because Olbers already had credit for discovering a planet (Pallas at the time, the asteroids were considered to be planets), he gave the honor of naming his new discovery to German mathematician Carl Friedrich Gauss, whose orbital calculations had enabled astronomers to confirm the existence of Ceres, the first asteroid, and who had computed the orbit of the new planet in the remarkably short time of 10 hours. [36] [37] Gauss decided on the Roman virgin goddess of home and hearth, Vesta. [38]

Name Edit

Vesta was the fourth asteroid to be discovered, hence the number 4 in its formal designation. The name Vesta, or national variants thereof, is in international use with two exceptions: Greece and China. In Greek, the name adopted was the Hellenic equivalent of Vesta, Hestia ( 4 Εστία ) in English, that name is used for 46 Hestia (Greeks use the name "Hestia" for both, with the minor-planet numbers used for disambiguation). In Chinese, Vesta is called the 'hearth-god(dess) star', 灶神星 zàoshénxīng, naming the asteroid for Vesta's role, similar to the Chinese names of Uranus, Neptune, and Pluto. [e]

Upon its discovery, Vesta was, like Ceres, Pallas, and Juno before it, classified as a planet and given a planetary symbol. The symbol represented the altar of Vesta with its sacred fire and was designed by Gauss. [39] [40] In Gauss's conception, this was drawn in its modern form, it is . [f]

After the discovery of Vesta, no further objects were discovered for 38 years, and the Solar System was thought to have eleven planets. [43] However, in 1845, new asteroids started being discovered at a rapid pace, and by 1851 there were fifteen, each with its own symbol, in addition to the eight major planets (Neptune had been discovered in 1846). It soon became clear that it would be impractical to continue inventing new planetary symbols indefinitely, and some of the existing ones proved difficult to draw quickly. That year, the problem was addressed by Benjamin Apthorp Gould, who suggested numbering asteroids in their order of discovery, and placing this number in a disk (circle) as the generic symbol of an asteroid. Thus, the fourth asteroid, Vesta, acquired the generic symbol ④. This was soon coupled with the name into an official number–name designation, ④ Vesta, as the number of minor planets increased. By 1858, the circle had been simplified to parentheses, (4) Vesta, which were easier to typeset. Other punctuation, such as 4) Vesta and 4, Vesta, was also used, but had more or less completely died out by 1949. [44] Today, either Vesta, or, more commonly, 4 Vesta, is used.

Early measurements Edit

Photometric observations of Vesta were made at the Harvard College Observatory in 1880–1882 and at the Observatoire de Toulouse in 1909. These and other observations allowed the rotation rate of Vesta to be determined by the 1950s. However, the early estimates of the rotation rate came into question because the light curve included variations in both shape and albedo. [46]

Early estimates of the diameter of Vesta ranged from 383 (238) in 1825, to 444 km (276 mi). E.C. Pickering produced an estimated diameter of 513 ± 17 km (319 ± 11 mi) in 1879, which is close to the modern value for the mean diameter, but the subsequent estimates ranged from a low of 390 km (242 mi) up to a high of 602 km (374 mi) during the next century. The measured estimates were based on photometry. In 1989, speckle interferometry was used to measure a dimension that varied between 498 and 548 km (309 and 341 mi) during the rotational period. [47] In 1991, an occultation of the star SAO 93228 by Vesta was observed from multiple locations in the eastern United States and Canada. Based on observations from 14 different sites, the best fit to the data was an elliptical profile with dimensions of about 550 km × 462 km (342 mi × 287 mi). [48] Dawn confirmed this measurement.

Vesta became the first asteroid to have its mass determined. Every 18 years, the asteroid 197 Arete approaches within 0.04 AU of Vesta. In 1966, based upon observations of Vesta's gravitational perturbations of Arete, Hans G. Hertz estimated the mass of Vesta at (1.20 ± 0.08) × 10 −10 M ☉ (solar masses). [49] More refined estimates followed, and in 2001 the perturbations of 17 Thetis were used to calculate the mass of Vesta to be (1.31 ± 0.02) × 10 −10 M ☉ . [50] Dawn determined it to be 1.3029 × 10 −10 M ☉ .

Vesta orbits the Sun between Mars and Jupiter, within the asteroid belt, with a period of 3.6 Earth years, [7] specifically in the inner asteroid belt, interior to the Kirkwood gap at 2.50 AU. Its orbit is moderately inclined (i = 7.1°, compared to 7° for Mercury and 17° for Pluto) and moderately eccentric (e = 0.09, about the same as for Mars). [7]

True orbital resonances between asteroids are considered unlikely due to their small masses relative to their large separations, such relationships should be very rare. [51] Nevertheless, Vesta is able to capture other asteroids into temporary 1:1 resonant orbital relationships (for periods up to 2 million years or more) about forty such objects have been identified. [52] Decameter-sized objects detected in the vicinity of Vesta by Dawn may be such quasi-satellites rather than proper satellites. [52]

Vesta's rotation is relatively fast for an asteroid (5.342 h) and prograde, with the north pole pointing in the direction of right ascension 20 h 32 min, declination +48° (in the constellation Cygnus) with an uncertainty of about 10°. This gives an axial tilt of 29°. [53]

There are two longitudinal coordinate systems in use for Vesta, with prime meridians separated by 150°. The IAU established a coordinate system in 1997 based on Hubble photos, with the prime meridian running through the center of Olbers Regio, a dark feature 200 km across. When Dawn arrived at Vesta, mission scientists found that the location of the pole assumed by the IAU was off by 10°, so that the IAU coordinate system drifted across the surface of Vesta at 0.06° per year, and also that Olbers Regio was not discernible from up close, and so was not adequate to define the prime meridian with the precision they needed. They corrected the pole, but also established a new prime meridian 4° from the center of Claudia, a sharply defined crater 700 meters across, which they say results in a more logical set of mapping quadrangles. [54] All NASA publications, including images and maps of Vesta, use the Claudian meridian, which is unacceptable to the IAU. The IAU Working Group on Cartographic Coordinates and Rotational Elements recommended a coordinate system, correcting the pole but rotating the Claudian longitude by 150° to coincide with Olbers Regio. [55] It was accepted by the IAU, though it disrupts the maps prepared by the Dawn team, which had been positioned so they would not bisect any major surface features. [54] [56]

Vesta is the second-most-massive body in the asteroid belt, [58] though only 28% as massive as Ceres. [21] Vesta's density is lower than those of the four terrestrial planets, but higher than that of most asteroids and all of the moons in the Solar System except Io. Vesta's surface area is about the same as that of Pakistan, or Texas and North Carolina combined (about 800,000 square kilometers). [g] It has a differentiated interior. [22] Vesta is only slightly larger ( 525.4 ± 0.2 km [9] ) than 2 Pallas ( 512 ± 3 km ) in volume, [59] but is about 25% more massive.

Vesta's shape is close to a gravitationally relaxed oblate spheroid, [53] but the large concavity and protrusion at the southern pole (see 'Surface features' below) combined with a mass less than 5 × 10 20 kg precluded Vesta from automatically being considered a dwarf planet under International Astronomical Union (IAU) Resolution XXVI 5. [60] A 2012 analysis of Vesta's shape [61] and gravity field using data gathered by the Dawn spacecraft has shown that Vesta is currently not in hydrostatic equilibrium. [9] [62]

Temperatures on the surface have been estimated to lie between about −20 °C with the Sun overhead, dropping to about −190 °C at the winter pole. Typical daytime and nighttime temperatures are −60 °C and −130 °C respectively. This estimate is for 6 May 1996, very close to perihelion, although details vary somewhat with the seasons. [14]

Geologic map of Vesta [63]
The most ancient and heavily cratered regions are brown areas modified by the Veneneia and Rheasilvia impacts are purple (the Saturnalia Fossae Formation, in the north) [64] and light cyan (the Divalia Fossae Formation, equatorial), [63] respectively the Rheasilvia impact basin interior (in the south) is dark blue, and neighboring areas of Rheasilvia ejecta (including an area within Veneneia) are light purple-blue [65] [66] areas modified by more recent impacts or mass wasting are yellow/orange or green, respectively.

Prior to the arrival of the Dawn spacecraft, some Vestan surface features had already been resolved using the Hubble Space Telescope and ground-based telescopes (e.g. the Keck Observatory). [67] The arrival of Dawn in July 2011 revealed the complex surface of Vesta in detail. [68]

Rheasilvia and Veneneia craters Edit

The most prominent of these surface features are two enormous craters, the 500-kilometre (311 mi)-wide Rheasilvia crater, centered near the south pole, and the 400 km (249 mi) wide Veneneia crater. The Rheasilvia crater is younger and overlies the Veneneia crater. [69] The Dawn science team named the younger, more prominent crater Rheasilvia, after the mother of Romulus and Remus and a mythical vestal virgin. [70] Its width is 95% of the mean diameter of Vesta. The crater is about 19 km (12 mi) deep. A central peak rises 23 km (14 mi) above the lowest measured part of the crater floor and the highest measured part of the crater rim is 31 km (19 mi) above the crater floor low point. It is estimated that the impact responsible excavated about 1% of the volume of Vesta, and it is likely that the Vesta family and V-type asteroids are the products of this collision. If this is the case, then the fact that 10 km (6.2 mi) fragments have survived bombardment until the present indicates that the crater is at most only about 1 billion years old. [71] It would also be the site of origin of the HED meteorites. All the known V-type asteroids taken together account for only about 6% of the ejected volume, with the rest presumably either in small fragments, ejected by approaching the 3:1 Kirkwood gap, or perturbed away by the Yarkovsky effect or radiation pressure. Spectroscopic analyses of the Hubble images have shown that this crater has penetrated deep through several distinct layers of the crust, and possibly into the mantle, as indicated by spectral signatures of olivine. [53]

The large peak at the center of Rheasilvia is 20 to 25 km (12–16 mi) high and 180 km (112 mi) wide, [69] and is possibly a result of a planetary-scale impact. [72]

Other craters Edit

Several old, degraded craters rival Rheasilvia and Veneneia in size, though none are quite so large. They include Feralia Planitia, shown at right, which is 270 km (168 mi) across. [73] More-recent, sharper craters range up to 158 km (98 mi) Varronilla and 196 km (122 mi) Postumia. [74]

"Snowman craters" Edit

The "snowman craters" is an informal name given to a group of three adjacent craters in Vesta's northern hemisphere. Their official names from largest to smallest (west to east) are Marcia, Calpurnia, and Minucia. Marcia is the youngest and cross-cuts Calpurnia. Minucia is the oldest. [63]

Troughs Edit

The majority of the equatorial region of Vesta is sculpted by a series of parallel troughs. The largest is named Divalia Fossa (10–20 km wide, 465 km long). Despite the fact that Vesta is a one-seventh the size of the Moon, Divalia Fossa dwarfs the Grand Canyon. A second series, inclined to the equator, is found further north. The largest of the northern troughs is named Saturnalia Fossa (≈ 40 km wide, > 370 km long). These troughs are thought to be large-scale graben resulting from the impacts that created Rheasilvia and Veneneia craters, respectively. They are some of the longest chasms in the Solar System, nearly as long as Ithaca Chasma on Tethys. The troughs may be graben that formed after another asteroid collided with Vesta, a process that can happen only in a body that, like Vesta, is differentiated. [75] Vesta's differentiation is one of the reasons why scientists consider it a protoplanet. [76]

Surface composition Edit

Compositional information from the visible and infrared spectrometer (VIR), gamma-ray and neutron detector (GRaND), and framing camera (FC), all indicate that the majority of the surface composition of Vesta is consistent with the composition of the howardite, eucrite, and diogenite meteorites. [77] [78] [79] The Rheasilvia region is richest in diogenite, consistent with the Rheasilvia-forming impact excavating material from deeper within Vesta. The presence of olivine within the Rheasilvia region would also be consistent with excavation of mantle material. However, olivine has only been detected in localized regions of the northern hemisphere, not within Rheasilvia. [32] The origin of this olivine is currently unknown.

Features associated with volatiles Edit

Pitted terrain has been observed in four craters on Vesta: Marcia, Cornelia, Numisia and Licinia. [80] The formation of the pitted terrain is proposed to be degassing of impact-heated volatile-bearing material. Along with the pitted terrain, curvilinear gullies are found in Marcia and Cornelia craters. The curvilinear gullies end in lobate deposits, which are sometimes covered by pitted terrain, and are proposed to form by the transient flow of liquid water after buried deposits of ice were melted by the heat of the impacts. [64] Hydrated materials have also been detected, many of which are associated with areas of dark material. [81] Consequently, dark material is thought to be largely composed of carbonaceous chondrite, which was deposited on the surface by impacts. Carbonaceous chondrites are comparatively rich in mineralogically bound OH. [79]

There is a large collection of potential samples from Vesta accessible to scientists, in the form of over 1200 HED meteorites (Vestan achondrites), giving insight into Vesta's geologic history and structure. NASA Infrared Telescope Facility (NASA IRTF) studies of asteroid (237442) 1999 TA 10 suggest that it originated from deeper within Vesta than the HED meteorites. [23]

Vesta is thought to consist of a metallic iron–nickel core 214–226 km in diameter, [9] an overlying rocky olivine mantle, with a surface crust. From the first appearance of calcium–aluminium-rich inclusions (the first solid matter in the Solar System, forming about 4.567 billion years ago), a likely time line is as follows: [82] [83] [84] [85] [86]

Timeline of the evolution of Vesta
2–3 million years Accretion completed
4–5 million years Complete or almost complete melting due to radioactive decay of 26 Al, leading to separation of the metal core
6–7 million years Progressive crystallization of a convecting molten mantle. Convection stopped when about 80% of the material had crystallized
Extrusion of the remaining molten material to form the crust, either as basaltic lavas in progressive eruptions, or possibly forming a short-lived magma ocean.
The deeper layers of the crust crystallize to form plutonic rocks, whereas older basalts are metamorphosed due to the pressure of newer surface layers.
Slow cooling of the interior

Vesta is the only known intact asteroid that has been resurfaced in this manner. Because of this, some scientists refer to Vesta as a protoplanet. [87] However, the presence of iron meteorites and achondritic meteorite classes without identified parent bodies indicates that there once were other differentiated planetesimals with igneous histories, which have since been shattered by impacts.

Composition of the Vestan crust (by depth) [88]
A lithified regolith, the source of howardites and brecciated eucrites.
Basaltic lava flows, a source of non-cumulate eucrites.
Plutonic rocks consisting of pyroxene, pigeonite and plagioclase, the source of cumulate eucrites.
Plutonic rocks rich in orthopyroxene with large grain sizes, the source of diogenites.

On the basis of the sizes of V-type asteroids (thought to be pieces of Vesta's crust ejected during large impacts), and the depth of Rheasilvia crater (see below), the crust is thought to be roughly 10 kilometres (6 mi) thick. [89] Findings from the Dawn spacecraft have found evidence that the troughs that wrap around Vesta could be graben formed by impact-induced faulting (see Troughs section above), meaning that Vesta has more complex geology than other asteroids. Vesta's differentiated interior implies that it was in hydrostatic equilibrium and thus a dwarf planet in the past, but it is not today. [69] The impacts that created the Rheasilvia and Veneneia craters occurred when Vesta was no longer warm and plastic enough to return to an equilibrium shape, distorting its once rounded shape and prohibiting it from being classified as a dwarf planet today.

Regolith Edit

Vesta's surface is covered by regolith distinct from that found on the Moon or asteroids such as Itokawa. This is because space weathering acts differently. Vesta's surface shows no significant trace of nanophase iron because the impact speeds on Vesta are too low to make rock melting and vaporization an appreciable process. Instead, regolith evolution is dominated by brecciation and subsequent mixing of bright and dark components. [90] The dark component is probably due to the infall of carbonaceous material, whereas the bright component is the original Vesta basaltic soil. [91]

Some small Solar System bodies are suspected to be fragments of Vesta caused by impacts. The Vestian asteroids and HED meteorites are examples. The V-type asteroid 1929 Kollaa has been determined to have a composition akin to cumulate eucrite meteorites, indicating its origin deep within Vesta's crust. [28]

Vesta is currently one of only six identified Solar System bodies of which we have physical samples, coming from a number of meteorites suspected to be Vestan fragments. It is estimated that 1 out of 16 meteorites originated from Vesta. [92] The other identified Solar System samples are from Earth itself, meteorites from Mars, meteorites from the Moon, and samples returned from the Moon, the comet Wild 2, and the asteroid 25143 Itokawa. [29] [i]

In 1981, a proposal for an asteroid mission was submitted to the European Space Agency (ESA). Named the Asteroidal Gravity Optical and Radar Analysis (AGORA), this spacecraft was to launch some time in 1990–1994 and perform two flybys of large asteroids. The preferred target for this mission was Vesta. AGORA would reach the asteroid belt either by a gravitational slingshot trajectory past Mars or by means of a small ion engine. However, the proposal was refused by the ESA. A joint NASA–ESA asteroid mission was then drawn up for a Multiple Asteroid Orbiter with Solar Electric Propulsion (MAOSEP), with one of the mission profiles including an orbit of Vesta. NASA indicated they were not interested in an asteroid mission. Instead, the ESA set up a technological study of a spacecraft with an ion drive. Other missions to the asteroid belt were proposed in the 1980s by France, Germany, Italy and the United States, but none were approved. [93] Exploration of Vesta by fly-by and impacting penetrator was the second main target of the first plan of the multi-aimed Soviet Vesta mission, developed in cooperation with European countries for realisation in 1991–1994 but canceled due to the dissolution of the Soviet Union.

In the early 1990s, NASA initiated the Discovery Program, which was intended to be a series of low-cost scientific missions. In 1996, the program's study team recommended a mission to explore the asteroid belt using a spacecraft with an ion engine as a high priority. Funding for this program remained problematic for several years, but by 2004 the Dawn vehicle had passed its critical design review [94] and construction proceeded.

It launched on 27 September 2007 as the first space mission to Vesta. On 3 May 2011, Dawn acquired its first targeting image 1.2 million kilometers from Vesta. [95] On 16 July 2011, NASA confirmed that it received telemetry from Dawn indicating that the spacecraft successfully entered Vesta's orbit. [96] It was scheduled to orbit Vesta for one year, until July 2012. [97] Dawn 's arrival coincided with late summer in the southern hemisphere of Vesta, with the large crater at Vesta's south pole (Rheasilvia) in sunlight. Because a season on Vesta lasts eleven months, the northern hemisphere, including anticipated compression fractures opposite the crater, would become visible to Dawn 's cameras before it left orbit. [98] Dawn left orbit around Vesta on 4 September 2012 11:26 p.m. PDT to travel to Ceres. [99]

NASA/DLR released imagery and summary information from a survey orbit, two high-altitude orbits (60–70 m/pixel) and a low-altitude mapping orbit (20 m/pixel), including digital terrain models, videos and atlases. [100] [101] [102] [103] [104] [105] Scientists also used Dawn to calculate Vesta's precise mass and gravity field. The subsequent determination of the J2 component yielded a core diameter estimate of about 220 km assuming a crustal density similar to that of the HED. [100]

Dawn data can be accessed by the public at the UCLA website. [106]

Observations from Earth orbit Edit

Albedo and spectral maps of 4 Vesta, as determined from Hubble Space Telescope images from November 1994

Elevation map of 4 Vesta, as determined from Hubble Space Telescope images of May 1996

Elevation diagram of 4 Vesta (as determined from Hubble Space Telescope images of May 1996) viewed from the south-east, showing Rheasilvia crater at the south pole and Feralia Planitia near the equator

Vesta seen by the Hubble Space Telescope in May 2007

Observations from Dawn Edit

Vesta comes into view as the Dawn spacecraft approaches and enters orbit:

Vesta from 100,000 km
(1 July 2011)

Vesta from 41,000 km
(9 July 2011)

In orbit at 16,000 km
(17 July 2011)

In orbit from 10,500 km
(18 July 2011)

The northern hemisphere from 5,200 km
(23 July 2011)

In orbit from 5,200 km
(24 July 2011)

In orbit from 3,700 km
(31 July 2011)

Full rotation
(1 August 2011)

Cratered terrain with hills and ridges
(6 August 2011)

Densely cratered terrain near terminator
(6 August 2011)

Vestan craters in various states of degradation, with troughs at bottom
(6 August 2011)

Hill shaded central mound at the south pole of Vesta
(2 February 2015)

True-color images Edit

Detailed images retrieved during the high-altitude (60–70 m/pixel) and low-altitude (

20 m/pixel) mapping orbits are available on the Dawn Mission website of JPL/NASA.

Its size and unusually bright surface make Vesta the brightest asteroid, and it is occasionally visible to the naked eye from dark skies (without light pollution). In May and June 2007, Vesta reached a peak magnitude of +5.4, the brightest since 1989. [107] At that time, opposition and perihelion were only a few weeks apart. [108] It was brighter still at its 22 June 2018 opposition, reaching a magnitude of +5.3. [109] Less favorable oppositions during late autumn 2008 in the Northern Hemisphere still had Vesta at a magnitude of from +6.5 to +7.3. [110] Even when in conjunction with the Sun, Vesta will have a magnitude around +8.5 thus from a pollution-free sky it can be observed with binoculars even at elongations much smaller than near opposition. [110]

2010–2011 Edit

In 2010, Vesta reached opposition in the constellation of Leo on the night of 17–18 February, at about magnitude 6.1, [111] a brightness that makes it visible in binocular range but generally not for the naked eye. Under perfect dark sky conditions where all light pollution is absent it might be visible to an experienced observer without the use of a telescope or binoculars. Vesta came to opposition again on 5 August 2011, in the constellation of Capricornus at about magnitude 5.6. [111] [112]

2012–2013 Edit

Vesta was at opposition again on 9 December 2012. [113] According to Sky and Telescope magazine, this year Vesta came within about 6 degrees of 1 Ceres during the winter of 2012 and spring 2013. [114] Vesta orbits the Sun in 3.63 years and Ceres in 4.6 years, so every 17.4 years Vesta overtakes Ceres (the previous overtaking was in April 1996). [114] On 1 December 2012, Vesta had a magnitude of 6.6, but it had decreased to 8.4 by 1 May 2013. [114]

2014 Edit

Ceres and Vesta came within one degree of each other in the night sky in July 2014. [114]

10. An Asteroid may have Killed the Dinosaurs

In fact, there is a theory prevalent among the scientific community that it was an asteroid that wiped out the dinosaurs. Many scientists believe that the epicenter of the mass extinction of the dinosaurs lies in the Chicxulub Crater, an impact crater that was discovered under the Yucatán Peninsula in Mexico.

Meteor Showers

Dates and tips on how and where to see "shooting stars" from meteor showers all over the world.

Estimation of average rock and asteroid mass associated with different stars - Astronomy

How hazardous are meteors, comets & asteroids?

The collisions of these objects with Earth are basically random events, but still we have some idea how often they happen.

Localized destruction happens every couple of hundreds of years and is somewhat equivalent to a hydrogen bomb. Last such event happened in 1908 near Tunguska river in Siberia. The number of casualties depends on the place of impact (the objects of this size usually explode in the air before reaching the ground, just like an atom bomb). If a city is struck, casualties could be close to a million, while Tunguska event had zero to one reported casualty (reports vary). An impact in the ocean would create a tsunami and definitely produce significant destruction on the nearby seaside. These events usually do not leave a crater and typically involve a 100-meter asteroid or comet.

A smaller object (around 20m diameter) struck Chelyabinsk Oblast in Russia and did cause over 1000 injuries. Most injuries occured when the blast destroyed windows and struck onlookers inside buildings who were looking at the fireball. Fortunately, there are no reported deaths from the Chelyabinsk impact.

A regional destruction happens at intervals on the order of 100,000 years, and devastates an area a size of a mid-sized country. One such event we know of is an impact that occurred 700,000 years ago in Southeast Asia. These events usually involve 1 km sized asteroids an leave a craters tens of kilometers across.

A global destruction happens less often than every 10 million years and involves an impact of 10 km asteroid making a 100+ km crater. K-T event, which caused the extinction of dinosaurs and other contemporary creatures falls into this category. The amount of destruction depends on the properties of rock in which the crater is being excavated. Unless acidic chemicals are released into the atmosphere such an impact does not necessarily have to produce a mass extinction. In any case, such an impact today would cause casualties among humans in the billions.

It is highly unlikely that a regional or global destruction would occur anytime soon (next couple of centuries) since we have already discovered most of near Earth asteroids larger than 1 km, and none of them seem to be heading this way. A localized impact has a less than a percent chance to happen in any given year, so the level of risk at any given place or time is also low.

Concerning smaller meteorites that hit the ground, they are a very low hazard and no human was ever reported being killed by a small meteorite (while one person was missing after Tunguska). I heard a story that a dog was killed by a meteorite that fell in 1911 in Nakhla, Egypt, and there were also instances of material damage. Still, traffic, pollution and even lightnings are much more dangerous than small meteorites.

Updated by Everett Schlawin on July 18, 2015.

About the Author

Matija Cuk

Matija works on the orbital dynamics of the lesser moons of Jupiter and Saturn. He graduated with his PhD from Cornell in November 2004 and is now working at the University of British Columbia in Canada.

NASA Asteroid Exploration (Asteroid Missions)

Here you can know brief information and facts about asteroid exploration missions by NASA.

NASA’s spacecraft Galileo took the very first image of an asteroid 951 Gaspra in 1991. It was the first asteroid visited by a spacecraft.

Whereas the second asteroid 243 Ida and its natural moon Dactyl was also seen by the Galileo probe of NASA in 1993. It was the first known asteroid that has a natural satellite.

The first dedicated spacecraft NEAR Shoemaker made by NASA for asteroid exploration. The robotic space probe NEAR stands for “Near-Earth Asteroid Rendezvous” which was launched in 1996 by NASA to study Near-Earth Asteroids (NEAs).

Space probe NEAR Shoemaker take the images of the ‘ 253 Mathilde’ asteroid in 1997 and orbited the ‘ 433 Eros’ asteroid. And finally, it landed on the surface of the Eros asteroid on 12 Feb 2001 and ended the journey.

Dawn spacecraft of NASA launched in 2007 and visited and explored one of the largest asteroid Vesta in 2011. After exploring for almost one year in 2012 it started its journey for the Ceres dwarf planet.

A mission of NASA asteroid study, OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) was launched in September 2016. The main goal of this mission is to visit and take a sample of the asteroid ‘ 101955 Bennu’. Bennu is a B-type near-earth asteroid which is a subtype of carbonaceous asteroids. NASA’s OSIRIS-REx is currently (in 2020) orbiting the earth asteroid Bennu and will return with the sample in 2023 .

Many other space agencies including NASA are researching the asteroids. According to scientists, asteroids can be used for bringing materials that are rare or extinct on earth. It is called asteroid mining . Asteroid mining can be useful for making space habitats or space colonization.

So these were some important information and overview of asteroids. Such as ‘what is asteroid’, types of asteroids, earth asteroids, NASA earth asteroids and missions, asteroid mining, and many more. I hope you have liked it and also do comment below your views for the asteroids.