More planet discoveries via microlensing!

[folkhemmet]

A paper just came out a few days ago on the astrophysics preprint archive which discusses the past, present, and future of planetary microlensing searches. Here is the title and author: Microlensing Searches for Planets: Results and Future Prospects B. Scott Gaudi Department of Astronomy, The Ohio State University

According to the author, the number of extrasolar planets found via microlensing has been increasing even if the results have not been published, yet. Specifically, he said: "With the recent MOA upgrade, the rate of planet detections has increased substantially. From 2003-2006, six planets were detected (four have been published). From the 2007 bulge season alone, there are four fairly secure planetary events. This rate can be expected to increase modestly as analysis techniques improve, and so the next several years should bring of order a dozen planet detections."

Microlensing searches already strongly suggest that approximately a third of the galaxy's single M dwarf stars have ~10 Me worlds between 1 and 4 A.U. These new discoveries should help shrink the large error bars associated with this statistic. After decades of ignorance and speculation, we are making great strides toward pinning down the value of Fp in the Drake equation. Very exciting!

[Kullat Nunu]

You already posted this on the exoplanet discoveries thread, but yeah, this is exciting paper.

Although our sample of microlensing planets is, uh, very limited, it is highly suggestive that Neptune- or super-Earth -type planets are very common. Even though they orbit red dwarfs in relatively distant orbits which makes them rigid, frozen super-Earths are more hospitable for life than Europa.

[folkhemmet]

Thanks for the reply, Kullat Nunu. Yes, I did post this on another thread, but I thought it would be more accessible if it was given its own thread.

I remember thinking back in the late 90s and early 2000s when microlensing results were all negative, oh no, maybe the Rare Earth hypothesis advocates (as well as others such as John Bally of University of Colorado) were right about planets being rare after all. Of course, planets being common would not be incompatible with their view that complex life is rare is the Universe, but they did use the apparent paucity of planets as one piece of evidence to buttress it. John Bally was of the view that the photoevaporation of protoplanetary disks, as observed in places such as the Orion Nebula, would lead to a small value for Fp in the Drake equation for two reasons: (i) the dust and gas would be "destroyed" before coalescing into planets, and (ii) about 90% of all stars are born in OB associations (a fancy way of saying "born in the midst of violent giant stars"). Another important implication of the recent microlensing results is that planets can form in abundance in crowded stellar environments such as the galactic bulge--this dovetails with the HST transit photometry results of searches for planets in the galactic bulge; together microlensing and the HST transit results tell us that from our location in the galaxy into the galactic bulge the percentage of stars with planets is more or less uniform. It also is yet another piece of evidence that the same chemical and physical processes that have occured in our solar system are at work elsewhere in the Universe.

[neilzero]

Yes, more accessible with it's own thread title. Micro seems strange for a lens bigger than Earth/ Is there another name for the proceedure? Planets more than 0.1 AU from a M-dwarf star will be very cold, but colonies may be practical. Neil

[StupendousMan]

Micro seems strange for a lens bigger than Earth/ Is there another name for the proceedure?

"Microlensing" is a term which is generally used in situations involving a lens of stellar mass which
deflects light rays by very small angles -- tiny fractions of an arcsecond.