Are ancient fossils polluting the atmospheres of dead stars?
The search for signs of life beyond earth is never ending. There are obvious things to look for, based on our idea of what life needs. Things like water, oxygen, methane and carbon dioxide are all not only important components of planetary habitability, they are also (on earth at least), closely tied in with the presence of life. Therefore, we look for these on exoplanets, in the hope of one day finding alien life somewhere. Science is very rarely as simple as that, and with astrobiology sometimes it's a matter not of seeing a bioindicator directly, (because so far we haven't), but of doing a little educated guess work.
Sometimes hopeful possibilities turn up in unexpected places.
A white dwarf star is a strange class of object, and fairly rare in the universe. What is it?
A typical star, such as our own sun spends most of its lifetime producing heat and light from the fusion of hydrogen. As it ages, Its supply of hydrogen diminishes, and fusion of heavier elements begins. Eventually, fusion within the star stops as it begins fusing iron. At this point, the outward pressure produced by fusion no longer counteracts the stars gravity and it implodes, destroying itself in a tremendous explosion called a supernova.
A white dwarf will occasionally form when a star, in the red giant phase of it's life sheds it's outer layers, leaving behind an inert object composed often of carbon and oxygen. A white dwarf is very small and dense, with gravity 350,000 times that on Earth. AND all of this is packed into an object roughly the size of a small city!
How are white dwarfs useful to astrobiologists?
In my last video I spoke of how researchers may be able to glean information about exoplanet composition by using spectroscopic analysis to examine impact ejecta. This same principle has already been employed with debris orbiting the white dwarf star SDSSJ1043+0855
Despite the fact that white dwarfs are essentially dead stars, many have been observed with clouds of debris and dust around them. It's likely that this debris is the remains of the white dwarfs former planetary system. With the sudden change in status of their parent star, with resulting changes in gravity, orbits decay or falter. Many of these planets have fallen apart, and have become clouds of dust. This material has been observed transiting many white dwarf stars.
It turns out that Rufus is encircled by a cloud of fragments and dust, much of which is trapped in it's upper atmosphere. In 2016 observers at the University of Montreal, Canada, found that Rufus is accreting the outer layers of a large, rocky object, which appears to be differentiated much like Earth or Ganymede. On a daily basis, they were able to see changes in the composition of material in the white dwarfs atmosphere. The findings were exciting.
Large amounts of carbon, in addition to calcium and oxygen. Sounds pretty dull, right, but here on Earth that combination of elements often manifests as calcium carbonate, which is the main component of limestone. Limestone is a mineral formed from the remains of shelled organisms, which produce their shells from: calcium carbonate.
What does that mean? Is there a limestone encrusted world breaking up in a decaying orbit and crumbling down towards oblivion? Was this now dead world home to some form of life that also employs calcium carbonate as clams and mussels do?
Obviously this find warrants a closer look, and future observation with the James Webb Space Telescope could confirm the presence of calcium carbonate polluting Rufus.
In the spirit of not jumping to conclusions, calcium carbonate can also have non biological origins. But there is definitely reason to examine this system further, and others like it. Again, this kind of finding also chimes in with the concept in my impacts video of using dust and debris from impacts to determine exoplanet compositions. We can't see them clearly yet, but now we can see INSIDE them! That could yield even more valuable information about the presence of life.
The Complex Kevin MacLeod (incompetech.com)
Licensed under Creative Commons: By Attribution 3.0 License
James Webb Space Telescope video:
White Dwarf System/Impact Animations: Universe Sandbox 2
Stock Footage: Pixabay