A Tight Little Planet System, Dancing to the Tune of Gravity

Careful measurements using information from the Kepler planet-hunting spacecraft has allowed astronomers to figure out one of the tightest and most synchronized planet systems ever found.

Kepler 80 is a dim star in the constellation of Cygnus the swan, 1100 light years away, that has five planets orbiting it. That by itself is not unusual -- astronomers have now discovered a number of stars with 7, 6, or 5 planets around them and more are likely to be discovered as time goes by. What IS unusual is how tightly these five planets all hug their star.

The five planets take one, three, four, seven and nine earth days to orbit the star. (Think about that, their year is 1, 3, 4, 7, or 9 DAYS! If you lived on the inner planet, you would be 365 of its years old after one Earth year had gone by.)

Even more interesting, the outer 4 planets have orbits that are synchronized -- they are in tune, you might say. They return to the same arrangement of their positions around their star every 27 days. This is called a gravitational resonance and it's something gravity prefers to do when bodies can exchange energy.

Think of gravity like your uncle who is careful with his money -- they both prefer arrangements that are cheap! For example, gravity, when it can, tries to make bodies round, because then the pull on every point on the surface is the same -- which is the arrangement that takes the least energy.

When objects in space move around or with each other in a synchronized way, where one orbit is related to the other with numbers like 1 to 2 or 2 to 3, this requires less energy too. Pluto, for example, shows an extreme example of such resonances: Pluto takes 6.4 Earth days to spin and Pluto's big moon Charon takes 6.4 days to orbit the dwarf planet. So Pluto's day and month are the same length. Charon also takes 6.4 days to spin, so we have a 1 to 1 to 1 resonance of these motions.

Calculations show that the planets dancing in resonance around Kepler 80 are rocky world like our own Earth, although at least some of its planets are 4 to 6 times Earth's size. Imagine these giant Earths whipping around that little star in Cygnus in 1 to 9 days, year in and year out, lining up every 27 days in a kind of cosmic dance. Nature seems to permit so many odd and wonderful line-ups of planets out there -- science fiction is having trouble catching up to science fact.

(Just for comparison, the innermost planet in our own planetary system, Mercury, takes 88 days to orbit the Sun, and it is much smaller than Earth. So we have no large planets tightly hugging our star -- but a number of other stars besides Kepler 80 show such tight arrangements.)

A Gorgeous New Hubble Image and News from Kepler

Scientists working with the Hubble Space Telescope have just released a magnificent new image of one my favorite astronomical objects -- the Horsehead Nebula, a great cloud of "cosmic dirt" in the constellation of Orion. What makes this image a little different from usual is that we are not seeing the tower of dust with visible light, but with heat-rays (what scientists call the "infra-red.") 

It is in such clouds of dust and gas that new stars and planets are being regularly born. Because dust can block regular light, infrared images like this allow us to peer deeper into these regions of star birth. This particular image is about 2.5 light years across (where each light year is about 6 thousand billion miles) -- so we are seeing a good-sized pillar of cosmic "raw material" here. (Yet the Horsehead is just a part of a much larger complex of gas and dust called the Orion Molecular Cloud, which is roughly 1500 light years away from us.)

You can see two recently born stars at the top ridge of dust in the Horsehead in this image, confirming that star birth is happening in this dusty clump. Note that the colors we see on this picture are not real (since these are rays our eyes are not sensitive to.) The colors were picked by Hubble scientists to give a sense of the dustiness of the Horsehead.

You can contrast this infrared picture with a visible-light Hubble image taken with the Hubble in 2000-2001:
http://hubblesite.org/newscenter/archive/releases/2001/12/image/a/

and with an image of a larger region around it taken with the Canada-France-Hawaii Telescope on the ground at:http://www.nasa.gov/multimedia/imagegallery/image_feature_89.html

Aren't they gorgeous images?

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In other news you may have read that the Kepler mission, photographing 150,000 stars regularly in its search for planets orbiting other stars, has found three more planets that are just a little larger than Earth and orbiting in the "habitable zone" of their stars -- where water could be warm enough to be liquid. 

For the full story, see: http://www.kepler.nasa.gov/news/index.cfm?FuseAction=ShowNews&NewsID=243

That page gives you access to the quick info, the paintings of what the planets might like, animation, etc. To get the story in a more organized way, scroll down toward the bottom and click on the link to the full NASA news release.

The gist of the discovery is that we are finding more and more planets that are roughly earth-like -- perhaps a bit bigger, not always around the same kind of star as our Sun -- but Earth-like in their temperatures and other conditions. The Kepler team said that the current discovery is just an appetizer. Many more such planets may be among the 2740 candidate planets Kepler found that they are still examining and not yet ready to confirm.