Rocks on exoplanets similar to those on Earth, says new study which mined data from white dwarfs
Scientists have found 4,073 exoplanets so far. Yet, there is no other planet that can host life like Earth. But there are planets with similar rocky interiors. And they may be more common in the universe, according to a new study which used data collected from white dwarfs to determine the composition of exoplanets that once orbited them.
NASA has found many earth-sized rocky exoplanets. There is a possibility that some of them may host life. So astronomers are trying to come up with methods that can look for molecules in the exoplanets' atmospheres that are commonly found on Earth.
But there are challenges. "Learning the composition of planets outside our solar system is very difficult," said co-author Hilke Schlichting, UCLA associate professor of astrophysics and planetary science.
"It is difficult to obtain detailed geochemical information and composition [interiors] about terrestrial-type exoplanets because we don’t have any samples to analyze," Schlichting told MEA WorldWide (MEAWW).
So they turned to white dwarfs -- dense, burned-out remnants of normal stars -- to get a sense of what the composition of the rocks in certain exoplanets that orbited these stars looked like. White dwarfs have a strong gravitational pull, which means they have the ability to pull heavy elements like carbon, oxygen and nitrogen to sink rapidly into their interiors, according to the study.
The source of these elements can be traced back to rocks from asteroids or fragments of rocky planets that crashed into white dwarfs.
"The white dwarf's large gravitational pull shreds the asteroid or planet fragment that is orbiting it, and the material falls onto the white dwarf. Observing a white dwarf is like doing an autopsy on the contents of what it has gobbled in its solar system," said Alexandra Doyle, a UCLA graduate student of geochemistry and astrochemistry, in a press release.
These elements can then be detected by telescopes that hunt for exoplanets. Building on the data from the telescopes, the group came up with a whole new method to analyze the elements in rocks from asteroids or rocky planet fragments that orbited the six white dwarf stars.
This allowed them to examine white dwarf stars that were between 200 light-years and 665 light-years away.
The results revealed that the rocks from these exoplanets were similar to those found on Earth and Mars.
"If I were to just look at a white dwarf star, I would expect to see hydrogen and helium," Doyle said. "But in these data, I also see other materials, such as silicon, magnesium, carbon and oxygen -- material that accreted onto the white dwarfs from bodies that were orbiting them."
Commenting on the study, Schlichting told MEAWW, "In the case of this study, we are obtaining a very specific, but also very fundamental, characteristic of the rocks - their state of oxidation, as these rocks are being accreted onto the white dwarfs. There is no other way to do this at present."
The study is good news for the search for life outside our solar system, according to Schlichting. "This work shows that at least some rocky exoplanets are likely to have rock chemistry very similar to that of Earth and hence could host surface environments similar to those that facilitated the origin and evolution of life on earth," she told MEAWW.
The results of the study were published in Nature.