Dawn’s Rheasilvia Basin Only 1 Billion Years Old

Southern Hemisphere
Mineral Distribution in the Southern Hemisphere of the Protoplanet Dawn
Image Credit: NASA / JPLCalTech / UCLA / MPS / DLR / IDA

Young Craters

The newest release of data from the Dawn mission to Vesta shows a very young impact basin, the mineralogy of the asteroid, and suggests that Vesta is a protoplanet.

The image above shows the mineralogy of the Southern Hemisphere of Vesta. It covers only the inner crater and highland region of the Rheasilvia Basin, compared with the elevation and gravity contour maps previously released.

David O’Brien from the Planetary Science Institute in Tucson, Arizona, is a Dawn mission scientists and discussed the dating of the two giant impact craters on the Southern Hemisphere of Vesta. “The large impact basins on the moon are all quite old. The fact that the largest impact on Vesta is so young was surprising.” Scientists have concluded that the Veneneia Basin is 2 billion years old, and the Rheasilvia Basin, which overlies Veneneia, was created only 1 billion years ago.

Vesta itself was created about 4.56 billion years ago. Observations by the Dawn spacecraft in the low mapping orbit of its year-long mission has revealed the layered composition that was suspected. Like the Earth, Mars, the Moon, and Mercury (see below), Vesta differentiated in a molten state, creating a crust, mantle and iron core. This qualifies Vesta as a protoplanet. But Vesta is not quite in the dwarf planet category to which the asteroid Ceres, next on Dawn’s agenda in 2015, or Pluto, belong.

Minerals and History

Minerals exposed in deep impacts show minerals related to subsurface magma. This adds to the evidence for a differentiated protoplanet.

Minerals on the surface of Vesta are rich in iron and magnesium, similar to pyroxenes. These minerals are the same as found in certain meteorites that have fallen on the Earth.

Southern Hemisphere
Mineral Distribution in the Southern Hemisphere of the Protoplanet Dawn
Image Credit: University of Tennessee

This image above shows three minerals in meteorites from Vesta.

The three meteorites were sliced and viewed through a polarizing microscope, which makes different minerals appear in different colors.

The image on the left is basaltic eucrite, from a meteorite named QUE 97053, from Antarctica. The middle image is cumulate eucrite from a meteorite found in Moore County, North Carolina. Finally, the right hand image is from a meteorite named GRA 98108, from Antarctica, and is composed of diogenite.

Protoplanet

Eucrites are mostly regolith minerals formed near the surface of Vesta under pressure from newer, overlying deposits.

Cumulate eucrites, however, are rare types with oriented crystals. They probably solidified in magma chambers deep within Vesta’s crust.

The crystals of diogenites are primarily magnesium based orthopyroxene, and are igneous rocks formed slowly, also deep within Vesta’s crust.

As such, these minerals are indicative of the molten nature of Vesta’s early history, and its status as a protoplanet.

Below, we have five of the smaller bodies in the Solar System: Mars, Mercury, Earth’s Moon, Ceres and Vesta. They show the progression from planet to dwarf planet to protoplanet.

All of this evidence suggests that Vesta is a protoplanet, a remnant left over from the formation of the rocky planets in the inner solar system. It was not swept up by the formation of those worlds.

Five Bodies
Five Solar System Bodies: Mars, Mercury, Earth’s Moon, Ceres and Vesta
Image Credit: NASA / JPL-CalTech / UCLA

The Dawn image gallery for Vesta is here.

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Oldest Recorded Supernova Remnant

RCW 86
RCW 86 Supernova Remnant Exploded 1800 Years Ago
Image Credit: NASA / JPL-Caltech / UCLA

In 185 AD, Chinese astronomers recorded a “guest star”. 1800 years later, astronomers determined that supernova remnant RCW 86, located about 8,000 light years from Earth, was the leftovers from the explosion of that “guest star”.

Seen from Earth, the remnant is larger across than our Moon. This is two to three times larger than expected for a supernova remnant of this age. That mystery has now been solved with new data from the Spitzer Space Telescope and the Wide-field Infrared Survey Explorer (WISE), as well as previous data from NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton Observatory. The findings have been published in the Astrophysical Journal by Brian J. Williams, et. al. Williams is an astronomer at North Carolina State University in Raleigh, North Carolina.

First, the explosion was a type 1a supernova. X-ray data from Chandra and XMM-Newton showed that the remnant contained a large proportion of iron, typical of a type 1a supernova.

Second, it seems likely that the remnant rapidly expanded into a “cavity” in space, thus greatly exceeding the usual progress of explosion material. The cavity was the result of a stellar wind blown by the late stages of the star prior to it becoming a white dwarf. This is unusual, and normally only seen in core-collapse supernovae (type 1b and 1c).

In the image above, red is associated with the dust in the blast wave of the supernova, dust in the background are yellow and green, and stars are blue.

Spacecraft Dawn and New Results from the Asteroid Vesta

Vesta
Elevation (left) and gravity contour (right) of the Asteroid Vesta
Image Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA

At the annual European Geosciences Union General Assembly from 22 – 27 April 2012 in Vienna, Austria, a series of papers on Dawn’s exploration of Vesta were presented, among 4,436 oral and 9,092 poster presentations in 530 unique scientific sessions together with 157 Poster Summaries & Discussions sessions as well as 165 side events.

A list of papers on Vesta can be found here.

The image above, left, shows the topography of Vesta’s southern hemisphere with the Rheasilvia Basin and the Veneneia Basin (a quadrangle map of Vesta can be found in this previous post).

The gravitational map on the right shows the gravitational field below the basins, with the gravity component from hills and valleys removed. Red shows the strongest gravitational pull, and blue the weakest. Rheasilvia has some denser material, shown in yellow, below the central peak, while the dark blue on the right rim of the basin may indicate lighter rock, or highly fractured material.

The image below shows a portion of Vesta and some of the many pockets of bright material on the asteroid. Vesta is one of the brightest objects in the solar system, and scientists conjecture that this represents original material from the formation of Vesta. The yellow boxes hightligh some of these bright pockets.

Bright Spots
Bright Albedo on the Asteroid Vesta
Image Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / UMD

A recent press release from NASA about the European Geosciences Union meeting details additional discoveries about Vesta, including temperature ranges in and out of shadows, surface mineral patterns, ancient rocks and recent dust and the 3-D gravitational fields from interior features of the protoplanet.

Launched in 2007, Dawn began its exploration of the approximately 530-kilometer-wide asteroid in mid-2011. The spacecraft’s next assignment will be to study the dwarf planet Ceres in 2015. These two icons of the asteroid belt have been witness to much of our solar system’s history.

Low Down on Vesta

Vesta
The South Pole of the Asteroid Vesta
Image Credit: NASA / JPLCalTech / UCLA / MPS / DLR / IDA

The Dawn spacecraft is beginning to wrap up its mission surveying Vesta. It completed the 70 day Low Altitude Mapping Orbit (LAMO) portion of its mission in December, January and February. The mission has been so smooth that the 40 days of reserve observation time have not been used. They will now be applied to the low altitude study of the composition of the surface and mapping of the gravity field. Dawn is currently about 210 kilometers above the surface.

We will discuss some of these low altitude images here. For a full description of the Dawn mission, see here (pdf). See also the nssphoenix articles on the mission, orbital capture, the rotation of Vesta, and previous low altitude images.

Below is a list of key dates for Dawn:

  • Launch – September 27, 2007
  • Mars gravity assist – February, 2009
  • Vesta arrival – July, 2011
  • Vesta departure – July, 2012
  • Ceres arrival – February 2015
  • End of primary mission – July 2015

In January, scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, completed models of the average global temperatures on the asteroid Vesta, and concluded that it is cold enough that ice could exist below the surface of the poles (see the article in the January 2012 issue of the journal Icarus).

Vesta is the second largest asteroid (after Ceres) in the belt between Mars and Jupiter. However, because of the axial tilt (27 degrees compared to Earth at 23 degrees), there are likely to be no locations where ice would remain frozen on the surface. This includes the 480 kilometer wide crater at the south pole (image above).

Below, left is Severina crater, a relatively young crater with sharp edges. It is approximately 25 kilometers in diameter located inc Vesta’s Rheasilvia quadrangle (see map at bottom), near Vesta’s south pole. On the rim is a newer small crater with sharp features.

Below, right is an older crater, degraded along the rim from bombardment from space. Many smaller young fresh craters pockmark the area, both inside and outside the old crater. The image was taken from an altitude of 272 kilometers, and is located in Vesta’s Oppia quadrangle.

Severina
Severina Crater on Vesta
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Smoothed Crater
Smoothed Crater on Vesta
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Below, left is Cornelia crater. Cornelia is a very young crater, about 15 kilometers in diameter, and located in Vesta’s Numisia quadrangle. The rim has partially collapsed, and the smooth surrounding area indicates that a large amount of fine-grained material was ejected during formation. The slumping material inside the crater is consistent with the fine-grained material in the ejecta.

Below, right, is a high resolution image of the surface in Vesta’s Oppia quadrangle, taken from an altitude of about 190 kilometers. Resolution is about 17.5 meters per pixel. The image is saturated with large and small craters, accumulated over billions of years. Sharp edged craters are young, and blurred, smoothed craters are old. Young craters are on top.

Cornelia
Cornelia Crater on Vesta
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

High Resolution
High Resolution Surface on Vesta
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Map of Vesta
Quadrangle Maps for the Asteroid Vesta
Image Credit: NASA/ JPL-Caltech/ UCLA/ MPS/ DLR/ IDA

Above is a quadrangle map of Vesta, showing the locations of quadrangles referred to in the article here. Additional maps can be found here.

Everything

Everything
The WISE
Image Credit: NASA / JPL-Caltech / UCLA

The Wide-field Infrared Survey Explorer (WISE) mission has just released the image above showing Everything in the infrared spectrum. Approximately 560 million stars, galaxies, gas clouds, near-Earth asteroids and other objects are included in the image.

Visible in the image:

  • Large and Small Magellanic clouds to the bottom right
  • The Andromeda galaxy forms a small blue streak to the lower left
  • The Rho Ophiuchi cloud complex, only 130 light years away, above the galactic center

Dawn In Low Altitude Orbit Above Vesta

Vesta
Dawn Image of Vesta from 230 kilometers
Image Credit: NASA / JPLCalTech / UCLA / MPS / DLR / IDA

The spacecraft Dawn has successfully reached its low orbit of 230 kilometers above the asteroid Vesta, for intense scientific research.

The primary instruments at this level will be the gamma ray and neutron detector (GRaND) and the gravity experiment. Currently, scientists expect Dawn to spend ten (10) weeks at this altitude. The objective is to determine the kinds of material (atoms) on the surface of Vesta and measure the gravitational field of the asteroid. Scientists want to determine the distribution of masses within Vesta.

Marc Rayman, Dawn’s chief engineer and mission manager based at NASA’s Jet Propulsion Laboratory, Pasadena, California noted:

Dawn has performed some complicated and beautiful choreography in order to reach this lowest orbit.” We are in an excellent position to learn much more about the secrets of Vesta’s surface and interior.

After this data collection period, Dawn will spiral outward to a new orbit around 680 kilometers above the surface for another high altitude mapping campaign. The Sun will then be higher in the northern regions of Vesta fir better imaging.

Dawn plans to leave Vesta in July 2012 and arrive at its second destination, the dwarf planet named Ceres, in February 2015.

Rosy Supernova Remnant

Puppis A
Puppis A Supernova Remnant by Wide-field Infrared Survey Explorer (WISE)
Image Credit: NASA / JPL-Caltech / UCLA

NASA has released images of the Supernova Remnant known as Puppis A. The massive star used up its hydrogen fuel and light from the explosion reached Earth about 3,700 years ago.

The Wide-field Infrared Survey Explorer (WISE), captured these images. As the star exhausted its fuel, it shed layers of gas and dust into the interstellar medium. The subsequent explosion and its shock wave are heating the gas and dust, creating the beautiful red glow seen in the image.

The green dust and gas in front of the rosy nebula are the result of an earlier supernova that exploded about 12,000 years ago. The Vela supernova remnant is about four times closer to Earth than is Puppis A.