Earth came early to the party in the evolving universe. According to a new theoretical study, when our solar system was born 4.6 billion years ago only eight percent of the potentially habitable planets that will ever form in the universe existed. And, the party won't be over when the sun burns out in another 6 billion years.
The bulk of those
planets — 92 percent — have yet to be born.
This conclusion is based on an assessment of data collected by NASA's
Hubble Space Telescope and the prolific planet-hunting Kepler space
observatory.
"Our main motivation was understanding the Earth's place in the
context of the rest of the universe," said study author Peter Behroozi
of the Space Telescope Science Institute (STScI) in Baltimore,
Maryland, "Compared to all the planets that will ever form in the
universe, the Earth is actually quite early."
Looking far away and far back in time, Hubble has given astronomers a
"family album" of galaxy observations that chronicle the universe's
star formation history as galaxies grew. The data show that the
universe was making stars at a fast rate 10 billion years ago, but the
fraction of the universe's hydrogen and helium gas that was involved
was very low. Today, star birth is happening at a much slower rate than
long ago, but there is so much leftover gas available that the
universe will keep cooking up stars and planets for a very long time to
come.
"There is enough remaining material [after the big bang] to produce
even more planets in the future, in the Milky Way and beyond," added
co-investigator Molly Peeples of STScI.
Kepler's planet survey indicates that Earth-sized planets in a star's
habitable zone, the perfect distance that could allow water to pool on
the surface, are ubiquitous in our galaxy. Based on the survey,
scientists predict that there should be 1 billion Earth-sized worlds in
the Milky Way galaxy at present, a good portion of them presumed to be
rocky. That estimate skyrockets when you include the other 100 billion
galaxies in the observable universe.
This leaves plenty of opportunity for untold more Earth-sized planets
in the habitable zone to arise in the future. The last star isn't
expected to burn out until 100 trillion years from now. That's plenty
of time for literally anything to happen on the planet landscape.
The researchers say that future Earths are more likely to appear
inside giant galaxy clusters and also in dwarf galaxies, which have yet
to use up all their gas for building stars and accompanying planetary
systems. By contrast, our Milky Way galaxy has used up much more of the
gas available for future star formation.
A big advantage to our civilization arising early in the evolution of
the universe is our being able to use powerful telescopes like Hubble
to trace our lineage from the big bang through the early evolution of
galaxies. The observational evidence for the big bang and cosmic
evolution, encoded in light and other electromagnetic radiation, will
be all but erased away 1 trillion years from now due to the runaway
expansion of space. Any far-future civilizations that might arise will
be largely clueless as to how or if the universe began and evolved.
The results will appear in the October 20 Monthly Notices of the Royal Astronomical Society.
Contact
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov
Peter Behroozi / Molly Peeples
Space Telescope Science Institute, Baltimore, Maryland
410-338-2458 / 410-338-2451
behroozi@stsci.edu / molly@stsci.edu
Source: HubbleSite
