Astronomy and Astrophysics

What cratered the Moon also destroyed a dwarf planet (Press Release)

Stowaways in a small car-sized asteroid that crashed in northern Sudan in 2008 have revealed what happened to a mysterious dwarf planet that is dusting Earth with a rare type of meteorites. That dwarf planet did not survive the “Late Heavy Bombardment” that cratered the Moon surface, an international team of researchers report in the latest issue of the journal Meteoritics and Planetary Science.

“The 2008 asteroid was a small chunk of a dwarf planet that once shattered into pieces,” says consortium lead Dr. Peter Jenniskens of the SETI Institute and NASA Ames Research Center. Jenniskens and co-author Dr. Muawia Shaddad recovered fragments of the asteroid, called 2008 TC3, by searching for meteorites with students of the University of Khartoum shortly after the fall in October of 2008. The recovered meteorites are named Almahata Sitta after the fall area in Sudan.

When the dwarf planet broke up, it left a debris field in the asteroid belt between Mars and Jupiter that now supplies a steady flow to Earth of the meteorites called ureilites. The dwarf planet is known as the Ureilite Parent Body. Ureilites contain very low levels of uranium, thorium and potassium, the elements that have long-lived radioactive isotopes, making it difficult for researchers to measure the times of catastrophic heating and disruption events for ureilites.

The asteroid 2008 TC3 was composed mostly of such ureilites, but had other meteorite types mixed in that had much higher levels of those long-lived radioactive isotopes. Those stowaways still contain the noble gases from radioactive decay and can thus provide clues to the collision history of the Ureilite Parent Body.

Now, Dr. Matthias Meier of the Department of Earth Sciences at the Swiss Federal Institute of Technology (ETH) at Zürich in Switzerland, working with Dr. Kees Welten of the Space Sciences Laboratory of the University of California at Berkeley and six co-authors, report the results of analysing the noble gases in two ordinary chondrites contained within asteroid 2008 TC3. They find that the two chondrite fragments were incorporated into the ureilite host very early in the solar system history, about 4.6 billion years ago.

“After that, the Ureilite Parent Body had its final large break-up event 3.8 billion years ago,” says Meier. Hence, the Ureilite Parent Body survived for 800 million years but was destroyed at about the same time that many of the craters on the Moon were formed in a period known as the “Late Heavy Bombardment”.

“Researchers think the Late Heavy Bombardment happened when the orbits of Jupiter and Saturn suddenly started to resonate,” says Jenniskens. “That happened when Jupiter ended up travelling around the Sun exactly in half the period that Saturn did.” The resonating of Jupiter and Saturn’s orbits dramatically changed the orbits of Uranus and Neptune and consequently scattered the comets just outside of the orbit of Neptune towards the inner solar system. Those comets hit the Earth and Moon and also many objects in the asteroid belt.

It now seems that a collision towards the end of the Late Heavy Bombardment shattered this dwarf planet into many smaller asteroids that are now supplying the ureilite meteorites that fall on Earth.

“It came as a big surprise to us that this collision happened so long ago,” says Jenniskens. “That explains why the debris field of this collision in the asteroid belt can be hiding in plain sight. We are now looking to identify a dynamically old family of asteroids as the source region of our ureilites and of asteroid 2008 TC3.”

 

ASTEROID FLY-BY REMINDS ASTRONOMERS TO BE VIGILANT

Mountain View, CA. Last night, a city-block sized asteroid did a fly-by of the Earth-Moon system. While there was no danger to our planet, Near Earth Asteroid (NEO) 2012 LZ1 was watched carefully by astronomers who track NEOs.

“Near Earth Asteroid 2012 LZ1, which was discovered in at an observatory in Australia just a week ago, flew past Earth Thursday evening at 14 times the distance to the Moon” noted Dr. David Morrison of  the SETI Institute.  “What sets this asteroid apart from others that cruise past the Earth is its large size. If an asteroid this large hit our planet, it could wipe out an area the size of state. This asteroid is in no danger of hitting now or in the foreseeable future, but someday that may well be its fate. This is why it is called a “potentially hazardous” asteroid. Astronomers will watch it closely to improve out knowledge of its orbit and to make sure it is not coming our way again soon.”

Morrison is a world-renown expert on NEOs. He is director of the Carl Sagan Center for Study of Life in the Universe at the SETI Institute, and former director of the NASA Lunar Science Institute and senior scientist at the NASA Astrobiology Institute, at NASA Ames Research Center in Mountain View, California. He is also the past Director of Space at NASA Ames. Morrison is credited as the founder of the multi-disciplinary field of astrobiology. Morrison is best known for his work in risk assessment of near Earth objects such as asteroids and comets. Asteroid 2410 Morrison was named in his honor for his work on the subject since 1991. Morrison also known for his "Ask an Astrobiologist" series on NASA’s website where he provides answers to questions submitted by the public about a variety of topics from 2012 doomsday hoaxes to planetary habitability discovery of extrasolar planets. He has published 12 books and over 150 papers primarily on Planetary Science, Astrobiology and Near Earth Object subjects

Morrison will be appearing at SETIcon II, a public conference hosted by the SETI Institute. He’s speaking on panels about asteroids, “Junkpiles or Resources for Future Generations” and “Cosmophobia: Doomsday and other Fiction Science”. SETIconII takes place June 22 – 24 at the Hyatt Santa Clara hotel in the heart of California’s Silicon Valley, and will feature approximately 50 panel discussions, fireside chats, and lightning talks.  Eminent guests from the worlds of science and science-fiction will be presenting at this unique event. For more information and registration, go to: seticon.org

Accredited journalists wanting to attend SETIcon can sign up for complimentary press registration with Curtis Sparrer at curtis.sparrer@graylingcp.com

Public Asked to Provide Information About the Meteor

MOFFETT FIELD, Calif. – NASA and the SETI Institute are asking the public for more information to help find amateur photos and video footage of the Sunday, April 22, 2012 meteor shower that illuminated the sky over the Sierra Nevada mountains.

NASA and SETI Institute scientists are seeking the photos and video footage to better analyze the trajectory of the meteorite and learn about its orbit in space.

NASA Ames and SETI Institute meteor astronomer Peter Jenniskens found a four-gram fragment of the meteor in a parking lot of Henningsen-Lotus Park, in Lotus, Calif., located on the American River not far from Sutter's Mill.

"This appears to be a rare CM-type chondrite, a primitive meteorite rich in organic compounds," Jenniskens said.

Persons who have photos or video of the meteorite are asked to contact Jenniskens at petrus.m.jennniskens@nasa.gov.  Media interested in interviewing Jenniskens and viewing the fragment are asked to contact Karen Randall of the SETI Institute at 650-575-2229.

AKARI FINDS CARBON MONOXIDE MOLECULES EMBEDDED IN TEN MILLION DEGREE GAS

A scientific team using the Japanese AKARI infrared space observatory finds carbon monoxide (CO) molecules in the ten million degree gas associated with the young supernova remnant Cassiopeia A (Cas A). The team is led by Dr. Jeonghee Rho, who holds a joint appointment at the SETI Institute, and at the SOFIA Science Center at NASA Ames Research Center (both located in Mountain View California). Theoretically it was neither predicted nor expected to find the carbon monoxide molecule associated with a highly energetic supernova remnant. Powerful electrons and heavy-element atoms produced by nuclear processes in supernovae should have destroyed these molecules. This finding could change our current understanding of the cycle of carbon and molecules in the interstellar gas and dust clouds.

Infrared spectra obtained by AKARI have detected a broad feature with a double-peaked profile (see Figure). A dozen spectra reveal CO features similar to this across the angular extent of Cas A. The CO emission is specially detected not only from the bright ring of shocked ejecta but also from the central region where unshocked ejecta are located. The CO at the center of Cas A contains material which has been relatively unchanged since a few years after the original supernova explosion. The spectral model applied to these spectra indicates that the broad feature is being composed of a few ten thousand spectral lines produced by CO (see Figure 1 right). Cas A is 330 years old and located at a distance of approximately 11 thousand light years in the direction of the well-known W-shaped constellation of Cassiopeia.

"When I saw these beautiful AKARI spectra, I was excited by the fact that carbon monoxide molecules are located within a ten million degree gas. It is like detecting CO molecules right at the center of the Sun. The Universe is full of surprises!" said Dr. Rho. CO molecules are common in space between stars, but these molecules are usually in a very cold state. The team captured signals from rare CO molecules that are warm (2000 K) and extremely dense (10 million molecules per cubic centimeter) by detecting this broad CO spectral feature in the infrared.

Observations from multiple space-based and ground-based observatories have been made in the discovery of CO in Cas A. An infrared image of Cas A that was made with NASA Spitzer Infrared Array Camera (IRAC) at a wavelength of 4.5 micronmeters unexpectedly showed bright emission from Cas A. This result led the authors to suspect that the emission may be produced by CO as well as the emission from other heavy elements. Follow-up near-infrared images with the Palomar Hale 5-meter (200-inch) telescope indicated a strong possibility that CO is present in Cas A. However, until AKARI detected CO through a spectroscopic observation, the presence of this molecule within this young supernova remnant could not be proved for certain.
 
By combining AKARI observations with the Spitzer image, "bullets" of CO molecules were shown to exist. These bullets have survived in the ten million degree gas of the 330 year-old supernova remnant. "The CO detection challenges our understanding of how molecules form in supernova ejecta and evolve with time. Are the CO molecules observed with AKARI produced after the explosion? Have they survived until now, sheltered in these clumps? Or can this warm CO have reformed in the remnant? Many intriguing questions arise from these very exciting observational data." said Professor Isabelle Cherchneff, a theoretician at the University of Basel in Switzerland.
 
Supernovae are one of major sources providing heavy elements to the interstellar medium; however, our finding implies that carbon is locked in CO and thus a lot of carbon is not free to return to the interstellar medium. If CO locks up C and O in molecular form, it is possible that other molecular species such as SiO lock up other heavy elements, too. Detecting CO molecules in supernova ejecta would change our understanding of astrochemistry, dust formation and the origin of huge quantities of dust observed in the early Universe.
 
AKARI (ASTRO-F) is an infrared astronomy satellite developed by Japan Aerospace Exploration Agency, in cooperation with institutes of Europe and Korea. It was launched on 21 February 2006. After its launch it was named AKARI which means “light” in Japanese. Its primary mission was to survey the entire sky in near-, mid- and far-infrared, through its 68.5 cm (27.0 in) aperture telescope.
 
The discovery of warm CO molecules with the AKARI Infrared Astronomical Satellite has just been published in the Astrophysical Journal Letters 747, Issue 1 on Feb 8, 2012 entitled "Spectroscopic Detection of Carbon Monoxide in the Young Supernova Remnant Cassiopeia A". Research team members in addition to Dr. Jeonghee Rho are Drs. Takashi Onaka at University of Tokyo, Jan Cami at University of Western Ontario, and William Reach at Universities Space Research Association.
 
  

THE BIZARRE CASE OF METEORS WITH TWO IDENTITIES

Astronomers have discovered why we see meteors flash through the night sky while they seemingly rain down on us gently at the same time. In a paper published in the December 20 issue of the Astrophysical Journal, models of the zodiacal cloud are reconciled with radar observations, revealing a game of hide and seek and an interesting identity switcharoo.

“This detective story was much a case of meteors you can see and those you can’t”, says lead author and planetary astronomer David Nesvorny of the Southwest Research Institute in Boulder, Colorado.

Meteors are caused by meteoroids that hit the Earth’s upper atmosphere at astronomical speeds, although some hit slower than others. Out in space, those meteoroids

move feverishly between the planets. They are seen as a diffuse glow of scattered sunlight in the night sky, called the zodiacal cloud.

While zodiacal cloud models predict that meteoroids should hit Earth relatively gently, raining down the micro-meteorites that lace the Antarctic snow, radar observations of meteors consistently see the sky filled with rapidly speeding ones, too fast for anything to survive.

“How is that possible?”, asked Nesvorny and his collaborators. “To reconcile things, we improved our model to predict meteor rates and took into account how radars are able to see meteors. And things worked!”

The new model showed that radars are nearly blind to slow meteors, but pick up just the right collection of fast meteors to explain what they see in nature.

One bizarre observation remained unexplained. Radars sensitive to small 100 micron sized sporadic meteors see the same speeds and approach directions as those sensitive to meteoroids ten times as big.

“That was a conundrum”, says meteor astronomer and co-author Peter Jenniskens of the SETI Institute and NASA Ames Research Center. “Bigger particles should disappear more quickly. Instead, they seem to survive for about the same time.”

In their new paper, Nesvorny and Jenniskens explain why: Meteoroids in the zodiacal cloud are born one way, and then turn into another after shedding most of their plumage.

Meteoroids are born from comets in a fragile form, prone to rapid destruction, most likely from heating and cooling in day-night cycles. These large centimeter-sized meteoroids cause the meteor showers we see at night. “Meteoroid streams don’t seem to survive for more than a few thousand years”, says Jenniskens.

They are broken into pieces a tenth to one millimeter in size that are observed as sporadic meteors by radar and as the diffuse zodiacal cloud in the night sky. It is those meteoroids that survive for almost 100,000 years before they are destroyed by collisions among themselves. “The radar data show that small and big ones are destroyed in this way at much the same rate”, concludes Nesvorny.

Co-authors on the paper include radar astronomer Diego Janches of the Space Weather Laboratory at NASA Goddard Space Flight in Greenbelt Maryland, as well as planetary astronomers David Vokrouhlicky, Petr Pokorny, and William F. Bottke of the South-West Research Institute. This work was supported by the NASA Planetary Geology and Geophysics and Planetary Astronomy programs. 

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