Reporting from day three of the American Astronomical Society meeting in Austin, Texas…

As you almost certainly already know, astronomers have found many, many planets in orbit around stars other than the Sun. My iPhone app tells me there are 725 such known extrasolar planets or “exoplanets.” With that many objects to study, and new ones being discovered like clockwork, astronomers have started to characterize different kinds of planets and planetary systems.

One nagging (well, intriguing) question is how many planets exist. Exoplanets certainly seem to be plentiful, but how plentiful, exactly? One of today’s announcements makes a bold claim:

Our Milky Way galaxy contains a minimum of 100 billion planets according to a detailed statistical study based on the detection of three extrasolar planets by an observational technique called microlensing. … [Our] galaxy contains a minimum of one planet for every star on average. This means that there is likely to be a minimum of 1,500 planets within just 50 light-years of Earth.

Well, okay, that’s exciting, and very possibly true, but note that phrase, “based on the detection of three extrasolar planets.” I like statistics as much as the next person, but a large gulf separates the numbers three and 100 billion. Looking at the abstract (brief summary) of the article online, I would draw attention to the uncertainty in the numbers they present—for example, they estimate that the percentage of stars with “super-Earths” (planets five to ten times as massive as Earth) effectively lies between 25% and 97%. That’s quite a range!

William Welsh, of San Diego State University, announced two new planets discovered by the Kepler mission, creatively named Kepler-34b and Kepler-35b. He described the planets as “fluffy Saturns,” far bigger than Earth and too close to their parent stars for liquid water to exist on their surfaces (well, if they have surfaces, cf. that “fluffy” descriptor). What makes them special? They both revolve around binary stars: in other words, each planet orbits two stars, which in turn revolve around one another.

Previously, the planet Kepler-16b had made news as “the real Tatooine” (at least that’s how we described it on Science Today back in September), making reference to the Skywalker clan’s home planet in Star Wars. So now we know of three such examples—a “new class of planetary systems,” in Welsh’s words—and astronomers expect to find many more.

Another Kepler announcement came from John Johnson at Caltech. Working with publicly available data, his team discovered an unusual little collection of planets: the smallest planets yet detected (all smaller than Earth, with the smallest about the size of Mars, the most compact system of planets ever discovered, and the least massive star known to harbor a planet (a red dwarf). A lot of firsts! Because the discoveries don’t come from the official Kepler team, they are designated KOI 961.03, KOI 961.02, and KOI 961.01 (where “KOI” stands for “Kepler Object of Interest”).

BTW, the parent star KOI 961 is only 70% larger than Jupiter, and indeed, the planets orbit the star in distances similar to the Jupiter system… So personally, I like the diagram that compares the system to Jupiter and its moons.

Johnson also fired off one of the better quips at the meeting: “transiting planets are like cockroaches—if you see one, you know there are others [you’re not seeing].” The reason? A planet only appears to transit its parent star from a particular vantage point, which means that for every one we observe to transit, there are presumably many more that we don’t see because the geometry isn’t quite right.

Also, on April 2nd, Johnson will speak at the Academy’s Morrison Planetarium as part of our Benjamin Dean Lecture Series. His talk, “The Quest for Habitable Planets Orbiting Red Dwarfs,” will give attendees an opportunity to learn more about KOI 961—as well as more exciting results to come!

Ryan Wyatt is the director of the Morrison Planetarium and Science Visualization at the California Academy of Sciences.

Reporting from day two of the American Astronomical Society meeting in Austin, Texas…

Much like people, stars live and die. But the processes of stellar birth and death present many mysteries for astronomers to resolve. Stars tend to form in clusters, in dense regions rich in gas and dust.

Joseph Hora, of the Harvard-Smithsonian Center for Astrophysics, described a detailed look at the star-forming region Cygnus X—and the Spitzer Science Center released a gorgeous, high-resolution image of the region to coincide with the announcement. (Today’s photo shows Robert Hurt, Visualization Scientist with Spitzer, describing details of the image displayed on a high-resolution power wall at the NASA science display.)

An infrared survey of about 25 square degrees (equivalent to the area of more than a hundred full moons) revealed nearly 26,000 possible “young stellar objects” (or YSOs), stars captured early in their evolution, still enshrouded by dense dust. The bright, young stars heat up all that dust, so astronomers look for excess emission in infrared light, and the high-resolution image allowed astronomers to find lots of (relatively) tiny objects and put them in context with the larger region. You can read more about the image and the discoveries in the official Spitzer press release.

Xavier Koenig, from NASA Goddard, presented infrared imagery from the Wide-field Infrared Survey Explorer (WISE) and described his work in studying how star formation is triggered inside one of these regions. Extremely massive stars tend to form first, near the center of a collapsing gas cloud, but what happens next can prove difficult to disentangle: stars don’t arrive on the scene with birth certificates, after all, so astronomers need to determine which ones formed when.

Koenig’s data suggest that the massive stars set of a chain reaction of star formation, with smaller stars forming outward from the center of a gas cloud. Or as the WISE team describes it:

The results suggest that stars are born in a successive fashion, one after the other, starting from a core cluster of massive stars and moving steadily outward.

Massive stars can also wreak havoc on their surroundings. Erick Young, science mission operations director for NASA’s Stratospheric Observatory For Infrared Astronomy (SOFIA),described observations of the W3 star-forming complex that reveal the effects of the stellar winds and radiation from the largest stars in the region. Eventually, all this activity will tear apart the very gas cloud that gave birth to the stars.

NASA describes the image in some detail:

The SOFIA observations reveal the presence of some 15 massive stars in various stages of their birth process. Toward the left of the inset image, a small bubble (arrow) has been cleared out of the gas and dust by the most massive star in this cluster. This bubble is surrounded by a dense shell (green) of material in which some of the dust and all of the large molecules have been destroyed. That shell is surrounded by mostly untouched cloud material, traced by the red emission from cooler dust. Astronomers have evidence that the expansion of such bubbles around massive newly born stars acts to compress nearby material and trigger the condensation of more stars.

SOFIA, by the way, has its home in California: headquartered at NASA Ames, the flying observatory takes off from the Dryden Aircraft Operations Facility in Palmdale. A 747SP equipped with a 2.7–meter telescope (and a big hole in the side of the aircraft), SOFIA flies high enough to make observations at wavelengths of light that don’t make it to Earth’s surface. And on February 6th, Erick Young will speak at the Morrison Planetarium as part of our Benjamin Dean Lecture Series, so attendees can learn more about the observatory—and star formation, I’m guessing—from Erick in person.

Ryan Wyatt is the director of the Morrison Planetarium and Science Visualization at the California Academy of Sciences.