More Earth-Like Worlds Than We Thought? Another Look

"Polluted Old Stars Suggest Earth-like Worlds May Be Common "
Space.com (April 12, 2010)

"Earth-like planets should be a fairly common feature of other solar systems in our galaxy, a new study of stellar senior citizens suggests.Earth-like planets should be a fairly common feature of other solar systems in our galaxy, a new study of stellar senior citizens suggests.

"More than 90 percent of stars in the Milky Way, including our own sun, end their lives as a white dwarfs. Traditionally, these dense stellar remains haven't been the first place that astronomers look for signs of planets outside our own solar system. Instead, exoplanet searches have focused on stars like our own sun.

"But tantalizing new results suggest that these elderly stars might also be a rich source of information on the potential for other planetary systems out there in the galaxy.More than 90 percent of stars in the Milky Way, including our own sun, end their lives as a white dwarfs. Traditionally, these dense stellar remains haven't been the first place that astronomers look for signs of planets outside our own solar system. Instead, exoplanet searches have focused on stars like our own sun...."

The short version, and an explanation for that "polluted old stars" headline, is that white dwarfs tend to have a whole lot more heavy elements in them than current models of stellar evolution say they should. They could have picked up these elements just by traveling through the interstellar medium for a really long time, but the mix of elements is hard to explain that way.

One of the simpler explanations is that quite a lot of rock fell on these stars, after they became white dwarfs. One of the places you're likely to get rocks is from planets and asteroids - which suggests that these old stars may have had planets at one time.

Since we go with the assumption that things change, but don't change all that much, it's not unreasonable to think that if a lot of stars had planets a long time ago, a lot of stars have planets now.

A closer look at some of these white dwarfs, to see if there are traces of oxygen on or around them, will have to wait until these researchers get time with the Hubble telescope.

I'm about as sure as I can be, that this isn't the final word on exoplanets. A few months ago another survey found evidence for fewer planets than expected. (January 9, 2010)

As I've said - a lot - these are interesting times.

Related posts:

• "Planets Found Circling Other Stars: 429 So Far"
  (February 15, 2010)
• ""Alien Dust," HD 131488, and the Puzzle of Planets"
  (January 15, 2010)
• "Early Returns From Galactic Census: Not As Many Planets as Expected"
  (January 9, 2010)

More:

• "A Serious Search for Other Worlds, Life, and - Maybe - Extra-Terrestrial Intelligence"