STScI: Most Earth-Like Worlds Have Yet to Be Born

[bystander]

Most Earth-Like Worlds Have Yet to Be Born
Royal Astronomical Society | STScI HubbleSite | 2015 Oct 20

[img3="Artist's Concept of Earth-Like Planets in the Future Universe
Credit: NASA, ESA, and G. Bacon (STScI)"]http://imgsrc.hubblesite.org/hu/db/imag ... ge_web.jpg[/img3][hr][/hr]

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. ...

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. ...

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. ...

On The History and Future of Cosmic Planet Formation - Peter Behroozi, Molly Peeples

• Monthly Notices of the RAS 454(2):1811 (2015 Dec 01) DOI: 10.1093/mnras/stv1817
  arXiv.org > astro-ph > arXiv:1508.01202 > 05 Aug 2015

[Ann]

Interesting, but I found this part confusing:

Royal Astronomical Society wrote:

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.

Yes, many dwarf galaxies still contain a lot of gas that can be used for future planet formation.

But giant galaxy clusters? There is a lot of gas in them, but this gas is hot and turbulent and not well suited for star formation or planet formation at all. What reason do we have to think that conditions inside giant galaxy clusters will be so different in the future?

Ann