On the first Tuesday of each month, I write an
astronomy-related column piece for the Oklahoman newspaper. On the following
day, I post that same column to my blog page.
This is reprinted by permission form the Oklahoman and www.newsok.com.
With nearly 4,000 known planets
orbiting other stars (exoplanets), a few questions inevitably come up from both
scientists and lay people alike: How similar are they to Earth? Do they have a composition
similar to our planet? Can they support life? The problem with answering these
questions is that exoplanets are tiny and extremely faint compared to the stars
they orbit. Any signal from them that might help answer these questions is
drowned out by the parent star.
Now, scientists have figured out
a way to answer one of those questions, that of the composition of other
planetary systems. We can’t directly measure the composition of the planets,
but as parent stars age and evolve, they present a way to determine planetary
composition.
When a sun-like star evolves to
its final state, a white dwarf, it contains almost nothing but hydrogen and
helium. As Dr. Siyi Xu of the Gemini Observatory in Hawaii and one of the
authors of the new study explained, “White dwarfs’ atmospheres are composed of
either hydrogen or helium, which give out a pretty clear and clean
spectroscopic signal. However, as the star cools, it begins to pull in material
from the planets, asteroids, comets and so on which had been orbiting it, with
some forming a dust disk, a little like the rings of Saturn. As this material
approaches the star, it changes how we see the star.”
Gemini South Observatory. Credit NSF
The star’s light shines through
the dusty rings allowing astronomers here on Earth to determine the composition
of the dust. It turns out, as Dr. Xu explains, “Most of the building blocks we
have looked at in other planetary systems have a composition broadly similar to
that of the Earth.” Such studies don’t yet tell us if the planets have water,
believed to be a prime ingredient necessary for life. But they reveal that
Earth’s overall composition is rather common. And since water is one of the
most abundant compounds in the universe, it seems likely that if other factors
are similar to our own solar system then water exits in those planetary systems
as well.
Dr. Robert Jedicke of the
University of Hawaii studies our moons. That’s right, plural. We are all quite
familiar with our big, bright Moon in the sky. But our solar system
occasionally picks up hitchhikers in the form of small asteroids that pass near
us. These mini-moons, as Dr. Jedicke calls them, allows us to study wandering
asteroids to get a better look at them than we can from their distance in the Asteroid
Belt. Not only will we learn more about them, Dr. Jedicke tells us they offer
an even more exciting possibility. "Mini-moons are perfect targets for
bringing back significant chunks of asteroid material, shielded by a
spacecraft, which could then be studied in detail back on Earth." Such
access to asteroids opens up both scientific and, possibly, financial
opportunities, as asteroids contain significant amounts of precious metals and,
perhaps more importantly, rare-earth metals, essential for our computer
technology.
