And Then There Were 400

At an international conference on extrasolar planets being held in Portugal, a group of European astronomers unveiled on Monday a list of 30 new exoplanets and two brown dwarfs orbiting more-or-less Sun-like stars. This brings the known exoplanet catalog to a total of 403 worlds.

The new additions were all found by the radial-velocity wobbles that they induce in their host stars, as detected by the HARPS planet-hunting spectrograph on the European Southern Observatory's 3.6-meter telescope at La Silla, Chile.

The European astronomers say that HARPS can measure a star's radial-velocity patterns with an accuracy as fine as 1 meter per second: slow walking speed. This would put HARPS at the head of the accuracy list in the hotly competitive world of exoplanet hunting. Such precision is essential for detecting relatively low-mass planets — not just "super-Jupiters," "Jupiters," and "Saturns" of other stars, but the "Neptunes" and "super-Earths" that are at the limits of current technology.

According to a press release from the European Southern Observatory about the new finds, "HARPS has facilitated the discovery of 24 of the 28 planets known with masses below 20 Earth masses. As with the previously detected super-Earths, most of the new low-mass candidates reside in multi-planet systems, with up to five planets per system."

In particular, says Stephane Udry (Geneva Observatory), the HARPS project suggests that at least 40% of solar-type stars have these smaller planets. "These low-mass planets are everywhere basically."

Limits of Technology

To extract the very slight, periodic radial-velocity changes in a star that signify an orbiting planet, astronomers have to subtract out the much larger continual changes caused by the telescope's own motion on the rotating Earth, Earth's curving motion around the Sun (at about 30,000 meters per second), and even the gravitational influences of the Moon and our solar system's other planets on Earth. All these effects are precisely known. But there may be trickier confounding factors on the distant star itself, such as surface turbulence or starspots that mimic a change in the star's radial-velocity signature as the star's rotation carries the spots around.

Nevertheless, astronomers don't think they've yet hit the fundamental limits of the radial-velocity method for finding planets. For particularly good "quiet" stars, it may be possible to reach accuracies measured in centimeters per second, and thus planets as low-mass as Earth. Such hunts could become possible as early as next year.

Selections from the Harvest

What are the new planets and their stars like? The stars, according to a preliminary list, range from spectral type F6 to M: from somewhat larger and hotter, to much cooler and dimmer than the Sun. The orbiting objects have minimum masses (not necessarily the true mass, but probably not too far off) ranging from 53 down to 0.017 Jupiters. That's from 17,000 down to 5 Earth masses. Their announced orbital periods range from 4 days to 13 years (though HARPS has only been working for five years).

Of special note, three of the planets orbit stars with a lower proportion of heavy elements than are in the Sun — with a "metallicity" of only 1/3 to 1/2 the Sun's. It's well known that the greater a star's metallicity, the more likely it is to have planets detectable. A subgroup of the European astronomers targeted low-metallicity stars in particular, and their finds confirm that planets do sometimes form in a moderately heavy-element-poor environment. Clearly more than this one factor is at work in determining whether a star will have planets, even big ones.

Several systems also show radial-velocity hints of additional objects in longer-period orbits that will require years of further tracking to confirm.

Here's the ESO press release.

Here's the Extrasolar Planets Catalog reordered so the new discoveries form the top of the list.

P.S.: Don't expect the total to stay near 400 for too long. The Kepler mission should announce a whole flotilla of transiting exoplanets in the coming months.

December 21, 2012

In case you haven't heard, there's a piece of hysteria going around (pumped up by movie marketing) that the world will end on December 21, 2012, supposedly based on astronomy and an ancient Mayan prediction.

Did the Mayans really think this? Is the astronomy for real ?  Do we actually have anything to worry about ?  The answers, not surprisingly, are "no," "no," and "of course not."

To make a long story short, December 21, 2012, really is a big flip-the-page date in the ancient Mayans' calendar. But there's no evidence that they believed the world would end then, and a fair amount of evidence to the contrary. Not that it would matter if they did. As for the planetary and galactic lineups that latter-day doom-mongers have tried to associate with that date, they're flat-out wrong.

But you probably have friends and family who are getting nervous that America will crack apart into cookie crumbs, tsunamis will sweep over the Himalayas, Earth's poles will flip, and a secret invisible planet will smack us down like a bowling pin. And they will be turning to you, the astronomy person, to ask about it.

We have the stuff you need to tell them. Noted archaeoastronomer E. C. Krupp explains all the details, and the history of this mania, in the cover story of the November 2009 issue of Sky & Telescope, now available at a newsstand near you. You probably won't find it in your supermarket, but it should be on the magazine rack in any good bookstore. And if it's sold out, you can always subscribe!

Incidentally, in that same issue, S&T editor-in-chief Robert Naeye describes some cosmic catastrophes that actually could happen — and explains why they're not likely to strike in the next millennium or two. Humanity has more pressing things to worry about.

P.S. A tidbit from Krupp's article: Boston University has a Center for Millennial Studies, and its director, historian Richard Landes, points out that throughout history, failed end-of-the-world movements have numbered in the "hundreds of thousands at least." There's never a shortage of people eager for everything to go kaput. Or at least to spin hoaxes about it.

For some interesting truth about December 21, 2012, check out my 2012 Learn The Truth Blog.

NASA Spacecraft Impacts Lunar Crater in Search for Water Ice

NASA's Lunar Crater Observation and Sensing Satellite, or LCROSS, created twin impacts on the moon's surface early Friday in a search for water ice. Scientists will analyze data from the spacecraft's instruments to assess whether water ice is present.

The satellite traveled 5.6 million miles during an historic 113-day mission that ended in the Cabeus crater, a permanently shadowed region near the moon's south pole. The spacecraft was launched June 18 as a companion mission to the Lunar Reconnaissance Orbiter from NASA's Kennedy Space Center in Florida.

"The LCROSS science instruments worked exceedingly well and returned a wealth of data that will greatly improve our understanding of our closest celestial neighbor," said Anthony Colaprete, LCROSS principal investigator and project scientist at NASA's Ames Research Center in Moffett Field, Calif. "The team is excited to dive into data."

In preparation for impact, LCROSS and its spent Centaur upper stage rocket separated about 54,000 miles above the surface of the moon on Thursday at approximately 6:50 p.m. PDT.

Moving at a speed of more than 1.5 miles per second, the Centaur hit the lunar surface shortly after 4:31 a.m. Oct. 9, creating an impact that instruments aboard LCROSS observed for approximately four minutes. LCROSS then impacted the surface at approximately 4:36 a.m.

"This is a great day for science and exploration," said Doug Cooke, associate administrator for the Exploration Systems Mission Directorate at NASA Headquarters in Washington. "The LCROSS data should prove to be an impressive addition to the tremendous leaps in knowledge about the moon that have been achieved in recent weeks. I want to congratulate the LCROSS team for their tremendous achievement in development of this low cost spacecraft and for their perseverance through a number of difficult technical and operational challenges."‪

Other observatories reported capturing both impacts. The data will be shared with the LCROSS science team for analysis. The LCROSS team expects it to take several weeks of analysis before it can make a definitive assessment of the presence or absence of water ice.

"I am very proud of the success of this LCROSS mission team," said Daniel Andrews, LCROSS project manager at Ames. "Whenever this team would hit a roadblock, it conceived a clever work-around allowing us to push forward with a successful mission."

The images and video collected by the amateur astronomer community and the public also will be used to enhance our knowledge about the moon.

"One of the early goals of the mission was to get as many people to look at the LCROSS impacts in as many ways possible, and we succeeded," said Jennifer Heldmann, Ames' coordinator of the LCROSS observation campaign. "The amount of corroborated information that can be pulled out of this one event is fascinating."

"It has been an incredible journey since LCROSS was selected in April 2006," said Andrews. "The LCROSS Project faced a very ambitious schedule and an uncommonly small budget for a mission of this size. LCROSS could be a model for how small robotic missions are executed. This is truly big science on a small budget."

Big Pix from Herschel

Europe's new Herschel Space Observatory is all checked out and in excellent working order, as the European Space Agency demonstrated this morning with its release of a gorgeous nebula picture.

With an aperture of 3.5 meters, Herschel is the largest space telescope yet flown (Hubble is 2.4 meters). Perhaps more importantly, Herschel works in the far-infrared part of the spectrum: a poorly explored realm between the familiar, shorter-wavelength "warm infrared" and the millimeter-wave and microwave radio bands. Its cameras can work at six far-infrared and submillimeter colors, with wavelengths around 70, 110, 160, 250, 350, and 500 microns. Such wavelengths are the ones most strongly emitted by objects that are extremely cold — not far above absolute zero.

What we see in the picture here (a mosaic of many small frames) is mostly very cold interstellar dust. It's not reflecting starlight but glowing with the characteristic, very weak thermal emission for such temperatures. Blue and green here represent two of Herschel's shorter wavelengths, highlighting less-cold dust. Red indicates longer wavelengths and colder material. Notice the bright points of star formation happening inside a few of the densest, coldest filaments, almost like pearls on a string.

This is just a taste. In the coming months and years there'll be lots more.