Tag: OSIRIS-REx

Asteroid Remains Around Dead Stars Reveal the Likely Fate of Our Solar System

Artist concept of an asteroid breaking up. (NASA/JPL-Caltech)

June 30th has been designated “Asteroid Day” to promote awareness of these small members of our solar system. But while asteroids are often discussed in the context of the risk they might pose to the Earth, their chewed up remains around other stars may also reveal the fate of our solar system.

It is 6.5 billion years into our future. The sun has fused hydrogen into a core of heavier helium. Compressed by its own gravity, the helium core releases heat and the sun begins to swell. It is the end of our star’s life, but what will happen to the solar system?

While very massive stars end their element-fusing days in a colossal explosion known as a supernovae, the majority of stars in our galaxy will take a less dramatic exit.

Our sun’s helium core will fuse to form carbon but there is not enough mass to achieve the crushing compression needed for the creation of heavier elements. Instead, the outer layers of the dying star will be blown away to leave a dense remnant with half the mass of our current sun, but squeezed down to the size of the Earth. This is a white dwarf; the most common of all stellar ends.

The life cycle of our sun

The white dwarf rapidly cools to become a dim twinkle in the sky. Within a few million years, our white dwarf will be less luminous that the sun today. Within 100 million years, it will be dimmer by a factor of 100. But examination of white dwarfs in our galaxy reveals this gentle dimming of the lights is not as peaceful as first appears.

The remnants of stars too light to fuse carbon, white dwarfs have atmospheres that should be thin shells of residue hydrogen and helium. Instead, observations have detected 20 different heavy elements in this envelope of gases that include rock-forming elements such as silicon and iron and volatiles such as carbon and nitrogen.

Infrared observations of over forty white dwarfs have additionally revealed compact dusty discs circling the dead stars. Sitting within the radius of a regular star, these could not have formed before the star shrank into a white dwarf. These must be the remains of what occurred as the star morphed from a regular fusion burner into a white dwarf.

This grizzly tale begins with the star’s expansion.… Read more

Ceres, Asteroids And Us

Ceres, as imaged by the spacecraft Dawn on a high altitude orbit 900 miles from the surface. The several bright spots on the asteroid have been of particular interest to scientists and are believed to contain salts and ice. The image is mosaic formed from a series of images.  (NASA/JPL-Caltech)

For most of us, asteroids exist primarily as a threat.  An asteroid that landed around the Yucatan peninsula, after all, is generally considered to have set into motion the changes that resulted in the elimination of the dinosaurs.

Other large in-coming asteroids laid waste to swaths of Siberia in 1908, dug the world’s largest crater (118 mile wide)  in South Africa long ago, and formed the Chesapeake Bay a mere 35 million years past.  And another large asteroid will almost certainly threaten Earth again some day.

There is, however, a reverse and possibly life-enhancing side to the asteroid story, one that is becoming more clear and intriguing as we learn more about them where they live.  Asteroids not only contain a lot of water — some of it possibly delivered long ago to a dry Earth — but they contain some pretty complex organic molecules, the building blocks of life.

The latest chapter in the asteroid saga is being written about Ceres, the largest asteroid in the solar system and recently declared to also be a dwarf planet (like Pluto.)

Using data from NASA’s Dawn spacecraft, a team led by the National Institute for Astrophysics in Rome and  the University of California, Los Angeles identified a variety of complex organic compounds, amino acids and nucleobases  — the kind that are the building blocks of life.  The mission has also detected signs of a possible subsurface ocean as well as cryovolcanos, which spit out ice, water, methane and other gases instead of molten rock.

“This discovery of a locally high concentration of organics is intriguing, with broad implications for the astrobiology community,” said Simone Marchi, a senior research scientist at Southwest Research Institute and one of the authors of the paper in Science. “Ceres has evidence of ammonia-bearing hydrated minerals, water ice, carbonates, salts, and now organic materials.”

He said that the organic-rich areas include carbonates and ammonia-based minerals, which are Ceres’ primary constituents.  Their presence along with the organics makes it unlikely that the organics arrived via another asteroid.

In an accompanying comment in the Feb. 16 edition of Science, Michael Küppers of the European Space Astronomy Center in Madrid makes the case that Ceres might once have even been habitable.… Read more

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