What I Learned Today

Finding planets? Old hat. What about finding moons?

It seems likely that planets around other stars might also be hosts to their own moons. In addition to just wanting to know what’s out there, detecting exomoons could have implications for the habitability of exoplanets. While gas giants themselves might not be habitable, their potential rocky moons could be, if the planet orbits in the habitable zone. Also, moons can help stabilize a planet’s orbital inclination over long time periods, making it easier for life to maintain its hold rather than experiencing dramatic oscillations in environmental conditions.

This video shows the expected effect that a moon could have on the light curves we observe remotely:

The Hunt for Exomoons – Lightcurve Demo from Alex Parker on Vimeo.

The effect here is quite noticeable because the moon is at high inclination (out of the plane of the planet’s rotation around its star).

HEK (the Hunt for Exomoons with Kepler) is a collaboration established with hopes of finding the first exomoon in Kepler data. They were successful in getting some crowdfunding from PetriDish.org to purchase a supercomputer for their search. Laudably, they plan to post numeric posterior results from their search as an aid to the community.

Exomoons are theorized to tweak the planet’s transit curve in a variety of ways, but they are subtle and in many cases can be confused with other causes (like interactions with other planets in the same system). The community is still working to develop reliable models.

So, no exomoons have yet been found — but it’s probably just a matter of time.

If you haven’t heard by now, the Kepler mission has opened up a firehose of exoplanet (candidate) detections. We’re up to more than 2300 candidates found by the mission, with more to come.

I’ve just discovered an awesome animation that Dan Fabrycky created to visualize systems discovered by Kepler that have more than one detected transiting exoplanet. (Note: this includes unconfirmed planet candidates as well.)

“There are 885 planet candidates in 361 systems. In this video, orbits are to scale with respect to each other, and planets are to scale with respect to each other (a different scale from the orbits). The colors are in order of semi-major axis. Two-planet systems (242 in all) have a yellow outer planet; 3-planet (85) green, 4-planet (25) light blue, 5-planet (8) dark blue, 6-planet (1, Kepler-11) purple.

I could stare at this for hours. Wow.

I attended an excellent talk today by David Hogg, a cosmologist at NYU, that was titled “A Comprehensive Model of All Astronomical Imaging Ever Taken.” Here I highlight just two of the interesting and thought-provoking topics that appeared in his talk.

Astrotagging: His group developed astrometry.net, a service that will analyze digital images of the night sky and automatically annotate them with identifiable stars. You can access this impressive service by uploading a photo to flickr and adding it to the group “astrometry,” as in this example. Automatically, astrometry.net analyzes all new images added to this group and adds a comment with all of the stars that were found, as well as marking them on the image itself. Clever, reliable, and useful! Nice work!

Milky Way orbits: Kepler deduced planetary orbits based on repeated observations of planetary positions. We know that our Sun, and the rest of the stars in our galaxy, also orbit around the Milky Way’s core. But those orbits are perturbed by the presence of dark matter, something we can’t observe directly, and anyway, it would take hundreds of millions of years just to observe one orbit. Could there be a short cut? If you look up at the sky in the right location you can find a “stream” of stars that mark out one such orbital tracks, where clumps of stars formed together but moved slightly apart, along their shared orbit. Hogg and colleagues came up with a 6-D description of an orbit fit to those observations, concluding that the best fit is “an eccentric orbit in a flattened isothermal potential.” For more details, see their paper: “Constraining the Milky Way Potential with a Six-Dimensional Phase-Space Map of the GD-1 Stellar Stream”. I wonder what this line of inquiry will end up telling us about that dark matter distribution?

How many moons does the Earth have? Just one, of course. But I recently learned that right now the Earth also has five natural quasi-satellites. The companion bodies orbit the Sun with the same period that the Earth does, but with a different eccentricity. Our five quasi-satellites are 3753 Cruithne, 2002 AA₂₉, 2003 YN₁₀₇, 2004 GU₉, and 2010 SO₁₆.

Here is a depiction of 3754 Cruithne’s orbit:

These orbits are not stable over the long term (with respect to the Earth) because they lie outside the Earth’s Hill sphere, its region of moon attraction. Eventually they’ll move on to other orbits. But for now, we have these five extra companions in our journey around the Sun.

The other day, I came across Observing With NASA, a site that lets anyone submit requests to a network of robotic telescopes. You pick a target and some simple observational settings, then submit your job — and the next day, you get an email with your results.

I had to try this out.

On March 17, I submitted a request to observe the moon, which seemed a good target since it would be nearly full. The next day, I received the excellent news that my image, that’s right, MY IMAGE OF THE MOON, was ready for accessing. Is it not beautiful?

You can also request images of the planets, stars, nebulae, and galaxies. I’m full of praise for this endeavor — what better way to let the public get involved with astronomy than by letting them select which observations to make? The website is easy to use and the results are rewarding. (You can download a FITS file with your data if you’d like to do more analysis, for which tools are also provided.)

Want to take your own picture with the Robotic Telescope Network? Click here!