Young Planets Remain Hot Longer than Assumed

An MIT scientist suggests young planets maintain a high temperature for several million years, much longer than previously assumed. This can make such planets easier to detect, because during this hot stage their brightness is not overshadowed by that of their parent stars. This long hot stage is caused by the rising of hot material within the planet to the surface.
MIT planetary scientist Linda Elkins-Tanton, Mitsui Career Development, Professor of Geology in the Department of Earth, Atmospheric, and Planetary Sciences, views profile showing that hot, young planets may be easier to spot because they stay hot longer than astronomers have thought. (Image credit: Donna Coveney)
MIT planetary scientist Linda Elkins-Tanton,
Mitsui Career Development, Professor
of Geology in the Department of Earth,
Atmospheric, and Planetary Sciences,
views profile showing that hot, young
planets may be easier to spot because
they stay hot longer than astronomers
have thought. (Image credit: Donna Coveney)

Planets orbiting stars are difficult to detect. Such planets reflect light from their parent stars but don’t emit any brightness of their own; on the other hand, the stars themselves are very bright. This large difference in brightness makes these planets quite elusive as they are overshadowed by their parent stars.

 
During the planets’ initial stages following formation, they are very hot. This makes them easier to detect as they stand out even relative to their bright parent stars. MIT planetary scientist Linda Elkins-Tanton at the Department of Earth, Atmospheric, and Planetary Sciences recently theorized that this hot period lasts much longer than previously assumed, creating a larger window of opportunity to detect these planets.
 
This extended period is caused by a two stage process. At first, the planet undergoes a short period of heating generated by a combination of radioactivity in the planet’s interior and the heat generated by the collision of millions of chunks of rock crashing together to form the planet. This stage lasts a mere few hundred thousand years, a very short astronomical period. Following this process, heavy iron-rich material at the planet’s surface sinks towards the core, inciting hot material in the planet to rise to the surface. This molten surface perseveres for millions, and even for tens of millions, of years.
 MIT planetary scientist Linda Elkins-Tanton, Mitsui Career Development, Professor of Geology in the Department of Earth, Atmospheric, and Planetary Sciences, views profile showing that hot, young planets may be easier to spot because they stay hot longer than astronomers have thought. (Image credit: Donna Coveney)
Artist’s impression of the Mercury Surface,
Space Environment, Geochemistry,
and Ranging (MESSENGER) spacecraft in
orbit around Mercury. (Image credit: NASA /
Johns Hopkins University Applied
Physics Laboratory / Carnegie
Institution of Washington).

A likely place to test out this theory is Earth. But due to the Earth’s crust being very dynamic, no relics of this stage were left over to be studied. Such remnants may be present on Mars or Mercury and perhaps will be available for study in the coming years. Elkins-Tanton’s study also resulted in conclusions regarding the composition of planets’ surfaces. Therefore, the detection of certain minerals on Mercury for example, can provide additional support to the new theory. The Messenger spacecraft is scheduled to begin a study of Mercury in 2011 and may assist in this task. Furthermore, detection of young planets in this hot stage around stars other than the Sun can also strengthen this conclusion.

 
Linda Elkins-Tanton presented her findings regarding this theory at the Oct. 14th annual meeting of the Division for Planetary Sciences of the American Astronomical Society. Her research was funded by the National Science Foundation and NASA’s Mars Fundamental Research Program.
 
TFOT reported on NASA’s endeavor to detect additional planets with the Multi-Object Apache Point Observatory Radial Velocity Exoplanet Large-Area Survey, whose goal is to massively search for new planets by observing about 11,000 nearby stars over 6 years. The research is due to begin in the last quarter of 2008 and scientists estimate that the project will find at least 150 new planets. In another related article TFOT reported on an analysis of Mercury’s surface, based on data collected in January 2008 by NASA’s Mercury Surface, Space Environment, Geochemistry, and Ranging spacecraft. The analysis has shown that Mercury’s volcanoes were involved in plain formation and suggest that its magnetic field is actively produced in the planet’s core. The new results put an end to a 30-years old argument regarding the origins of Mercury’s smooth plains and the source of its magnetic field.
 
Further information on the new research can be found in the MIT press release.