What I Learned Today

I’ve dabbled a little in cross-stitch embroidery, but never tackled anything this spectacular. beche-la-mer was so inspired by a topographical map of the Moon that she decided to embroider it, in full color and texture. After just one month’s effort, she achieved her goal.

You can read more about the process at her blog:

• The project begins
• The project complete

I think it’s awesome that she chose the far side of the Moon to immortalize.

(Thanks for the pointer, Jim!)

Jim suggests that a Mars follow-on would be another fun project. I think this image, showing the Tharsis bulge, Olympus Mons, and Valles Marineris, could make a particularly fine work of art:

But oh, all those French knots! Maybe I’ll finish the sock I’m knitting first.

Tune to the right radio frequency, and you can listen to Jupiter! Electrons passing through Jupiter’s magnetic field are accelerated and give off radio waves, a process called cyclotron radiation. The intensity varies with Jupiter’s longitude, and careful tracking of the radio waves has enabled a more precise estimate of Jupiter’s rotation period (previously estimated based on cloud features, which naturally are not stationary). NASA’s Radio Jove project encourages teachers, students, amateurs (and you) to listen in to Jupiter’s “broadcasts.” Here are examples of the two main radio burst types you might hear:

• L (long) burst from Jupiter
• S (short) burst from Jupiter

The frequency of the radio waves is proportional to the strength of the magnetic field. Jupiter’s frequency varies between 10 and 40 MHz, yielding “decametric” waves (where the wavelength is measured in tens of meters). Other planets would have different frequencies. In fact, there’s an ongoing effort to determine if we can detect known exoplanets via radio observations (with LOFAR or SKA)—and if so, then add this to the growing list of exoplanet detection techniques. As of today, we’re up to 353 exoplanets discovered… with more coming every day.

Two JPL astronomers have found another exoplanet, which is the first to be found using astrometry. That is, the presence of the planet was inferred by careful study of the host star to detect a very faint wobble (with respect to nearby stars) caused by the planet’s mass as it orbits the star. Unsurprisingly, this detection method works best when the mass of the planet is large relative to that of the star, and indeed, the VB 10 star (a red dwarf) is very small as stars go (1/10 the size of our Sun), and its planet is estimated as being nearly the same size as the star, although less massive. Surprisingly, this may actually be the first time the astrometry technique has borne fruit. All previous claims of planet detection by astrometry could not be verified using other methods. If this one succeeds, it will be the first. The challenge is that extremely high precision and multiple observations over the course of years (ideally, multiple orbits of the planet) are required to detect the extremely small planet-induced stellar motion. In this case, the discovery comes as the result of 12 years of observations by the Palomar Observatory.

You can read more details in the pre-print of the scientific paper, “An Ultracool Star’s Candidate Planet,” by Pravdo and Shaklan. I particularly like Figure 7, in which a Keplerian orbit for the planet is shown, modeled from the collected observations of stellar perturbations. The figure includes both error bars on the observations and lines connecting the observations to the corresponding points on the model. You can even watch a video of the observations of the star’s motion with an accompanying view of where in its orbit the planet would be (although this is a little confusing because the orbit is represented off to the side instead of traveling with the star). The effect is subtle enough, and the observations are spaced far enough apart, that I don’t see it with my eye (even stepping frame by frame), but that’s to be expected. Still, error bars and all, this is a fascinating hint at what might be going on in the vicinity of VB 10, and a definite motivation to obtain followup observations with other techniques (although it is a difficult target for the radial velocity and transit methods since the planet’s orbital plane is likely close to perpendicular from our perspective). The paper notes that it’s possible that other planets lurk in the same system — perhaps even in the habitable zone.

Clever astronomers have come up with many different, creative ways to detect extrasolar planets orbiting around other stars. We’re up to 346 planets detected now, by a variety of different methods including transit detection, radial velocity analysis, precision astrometry, and direct imaging. At the Missions for Exoplanets meeting today, I learned about another method that relies on serendipity but, when it happens, provides inarguable evidence for a planet.

Gravitational microlensing refers to the brief magnification we observe when a dimmer, closer star passes between us and a brighter, distant star. Gravitational effects cause the distant star to temporarily become even brighter (because its light is being bent and focused towards us). If the closer star (the “lensing” star) also has one or more planets, then the resulting light curve gets an extra bump from the planet’s “micro”-lensing effect.

Scott Gaudi of Ohio State University created this marvelous animation of microlensing in action, which also shows how it is detected. (I love the symbolic fraction!) The distant star is the red circle, the closer star is in orange, the distant star’s apparent position is in blue, and the closer star’s planet is the brown dot.

What’s neat about this phenomenon is that although no one yet seems up for predicting when and where it might happen next, as soon as the characteristic increase in brightness begins, teams across the globe are alerted and start watching, hoping to capture the planet’s bump (if any) when it happens. In fact, amateur observers have contributed key observational data that helped find a new planet.

Maybe I should break down and get a telescope already.

The EPOXI mission was born out of the desire to make use of the Deep Impact spacecraft, after it successfully hit Comet Tempel 1 with a separate smaller spacecraft. Two missions were selected to make use of Deep Impact: EPOCh (Extrasolar Planet Observations and Characterization) and DIXI (Deep Impact eXtended Investigation). If you stick DIXI and EPOCh together, you get… EPOXI. The proposers got kudos from NASA HQ for this acronym.

EPOCh has just finished its main investigation, which involved observing seven stellar targets that were believed to have planetary companions. I recently attended an excellent talk summarizing the results by Dr. Drake Deming, the deputy PI for EPOCh. They used Deep Impact’s camera to watch for the characteristic dip in stellar brightness when a planet transits across it. Since the camera was not designed for observing distant stars, it had no automatic stabilization, and the star would appear to wander all over the CCD. Tracking the star in the data once it was downlinked to Earth, and applying a different correction for each pixel in the CCD, makes ground processing challenging. However, they’ve been able to analyze this data and extract some interesting findings.

• They studied a Neptune-sized planet (radius about 4 times that of Earth) orbiting the red dwarf star GJ 436. It has an eccentric orbit that is likely to be influenced by a second, smaller planet. EPOCh has searched industriously for a signal from this smaller planet, so far not yet finding it (down to 1 Earth radius, the limit of what they can see with this instrument).
• A secondary transit happens when a planet goes behind its host star, from our perspective. This also causes a (smaller) dip in total brightness because the planet no longer reflects light from the star. This dip can help provide an upper bound on the albedo (brightness) of the planet. (Neat!)
• They also observed the Earth from Deep Impact, treating it as if it were an exoplanet and trying to see if they could accurately infer its properties. These observations serve as the perfect validation set to help us do a good job of interpreting similar observations of other planets, when we get to the point of having them. More details will appear in a paper on this subject of how an alien observer would view planet Earth.

Even better, the data collected by EPOCh will be released to the public in the spring. So you can try your hand at analyzing it, too!

And of course, stay tuned for news from the Kepler mission, set to launch on March 6. It will stare at (relatively) nearby stars specifically seeking Earth-sized planets in the “habitable zone” (where liquid water is stable). It will survey so many stars that even a null result (if they don’t find any Earth-sized planets) would make an interesting statement about the distribution of planets in the galaxy. It’s far more likely, though, that they will find such planets. We live in such exciting times!