Daily Archives: July 15, 2013

astronomy

New Horizons Spies Charon

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Pluto’s Largest Moon, Ahoy!

There be another moon, Captain!!

In a couple of years we’ll all be goggling over images from the New Horizons spacecraft as it whizzes through the Pluto system. Right now, the spacecraft is about 880 million kilometers from Pluto and closing in fast at a speed of 16.26 kilometers per second (relative to Earth). On July 1-3, the New Horizons Long Range Imager (LORRI) trained its eye on the distant dwarf planet to grab a snapshot of the system. The image it sent back showed Pluto quite clearly, and right next to it, the largest moon, Charon. The two worlds are about 19,000 kilometers away from each other, so at such a great distance, this is a pretty big milestone for the spacecraft’s imaging system.

Charon was officially discovered in 1978 by astronomer James Christy, who was using a 1.55-meter telescope at the U.S. Naval Observatory facility in Arizona. It’s a smallish world, measuring only about 1,200 kilometers across (about half the size of Pluto). The surface appears to be covered with water ice, and may be getting “refreshed” through the action of cryo-geysers venting material up from beneath the surface. That makes it an interesting world to explore in its own right, next to Pluto.

In case you haven’t been keeping up with the Pluto news (and really, who HASN’T been thinking about Pluto and its planetary status, eh?), New Horizons is a robotic mission set to explore Pluto and its five moons. It will sweep past at about 12,000 kilometers from Pluto’s surface and study the moons before heading out to explore other parts of the Kuiper Belt region of our solar system where Pluto and other dwarf planets orbit.  In October this year it will be just 5 astronomical units from Pluto.  (An astronomical unit is the distance between Earth and the Sun, 149.5 million kilometers). To give you some perspective on that distance, Jupiter and the Sun are just over 5 AU apart.

New Horizons was launched on its headlong rush out to the solar system deep-freeze on January 19, 2006. After it does its look-see at Pluto, Charon, Nix, Hydra, Kerberos and Styx, then the spacecraft will proceed to check out various frozen worlds called Kuiper Belt Objects before the expected end of its mission in 2026. If all goes well, and New Horizons continues to function, it will begin exploring the outer reaches of the heliosphere (the farthest reaches of the solar wind), in late 2038. Right now, the only spacecraft we’re getting data from in THAT part of the solar system are the Voyager 1 and 2 missions. So, stay tuned for more Pluto system news as it happens!

Hubble Space Telecope, neptune

It Was There All Along

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Hubble Space Telescope Images Reveal Neptune’s Moon

This composite Hubble Space Telescope picture shows the location of a newly discovered moon, designated S/2004 N 1, orbiting the giant planet Neptune, 4.8 billion kilometers from Earth. The moon is so small (no more than 12 miles across) and dim, it was missed by NASA’s Voyager 2 spacecraft cameras when the probe flew by Neptune in 1989. Several other moons that were discovered by Voyager appear in this 2009 image, along with a circumplanetary structure known as ring arcs. The black-and-white image was taken in 2009 with Hubble’s Wide Field Camera 3 in visible light. Hubble took the color inset of Neptune on August 19, 2009. Credit: NASA, ESA, and M. Showalter (SETI Institute).

Neptune is the most distant planet in our solar system, which makes its systems of moons and rings a challenge to observe from Earth. These things are small and dim, even in Hubble Space Telescope images and data.

On July 1, Dr. Mark Showalter, a scientist at the SETI Institute in California, spotted something in Hubble images that hadn’t been seen before circling around the giant planet. Or least, it hadn’t been seen by human eyes. It was a small moon orbiting the planet about once every 23 hours. He was actually studying faint arcs (segments) of rings. “The moons and arcs orbit very quickly, so we had to devise a way to follow their motion in order to bring out the details of the system,” he said. “It’s the same reason a sports photographer tracks a running athlete—the athlete stays in focus, but the background blurs.”

It turns out that this little moon, now dubbed S/2004 N1, was in images taken by Hubble between 2004 and 2009, but it’s extremely small and dim. It’s likely no one was looking directly for that moon, so it remained hidden in the data archives, waiting for Dr. Showalter to find it.

This finding is a great example of archival discoveries—that is, findings made as astronomers go back through earlier observations. They do this for a variety of reasons. Sometimes it’s to check and see if the object ever appeared to observers before. Or, as in the case of a supernova explosion, to see what the object that exploded looked like in earlier observations. Or, sometimes, they do it to chart change over time (for example, changes on the surface of Mars).

Prior observations of astronomical objects through the world’s panoply of telescopes (both ground-based, orbiting, and in situ (at planets) give us a good feel for how the planets, moons, rings, and distant objects like stars, nebulae, and galaxies change over time. The universe is a constantly evolving place, and it will always provide us with new objects and events to discover and study.