NASA Prepares for Asteroid’s Close Pass by Earth

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On Tuesday, November 8, at 6:28 p.m. EST, an asteroid the size of an aircraft carrier will soar past our planet at a distance closer than the Moon… and NASA scientists will be watching!

2005 YU55, a 400-meter (1,300-foot) -wide C-type asteroid, was discovered in December 2005 by Robert McMillan of the Spacewatch Program at the University of Arizona, Tucson. It’s pretty much spherical in shape and dark – darker than charcoal, in fact! Scientists with NASA’s Near-Earth Objects Observation Program will begin tracking it on November 4 using the 70-meter radar telescope at the Deep Space Network in Goldstone, California , as well as with the Arecibo Planetary Radar Facility in Puerto Rico beginning November 8. They will continue tracking 2005 YU55 through November 10.

Animation of 2005 YU55's trajectory on Nov. 8. (NASA/JPL) Click to play.

YU55’s orbit is well understood by scientists. It has come this way before, and although this is the closest it’s come to Earth in at least two centuries it will still be at least 324,600 kilometers (201,700 miles) away at nearest approach. That’s about 85% of the distance to the Moon.

It will approach from the sunward side, making viewing in visible light difficult until after it’s made its closest pass.

Other than the excitement it will most likely cause amongst radar astronomers, 2005 YU55 will have no physical effect on our planet. (There have been some rumors circulating online about this particular asteroid’s upcoming pass, in regards to earthquakes and tidal fluctuations and atmospheric disturbances and other such nonsense… the bottom line is that, like the ill-fated comet Elenin, 2005 YU55 has never been known to pose any threat to Earth.)

“YU55 poses no threat of an Earth collision over, at the very least, the next 100 years,” said Don Yeomans, manager of NASA’s Near-Earth Object Program Office at JPL. “During its closest approach, its gravitational effect on the Earth will be so miniscule as to be immeasurable. It will not affect the tides or anything else.”

The 70m telescope at the Goldstone Deep Space Communications Complex in California's Mojave Desert. (NASA/JPL)

Scientists are very eager though to have a prime opportunity to study this quarter-mile-wide world as it makes its closest pass. The giant telescopes at Goldstone and Arecibo will bounce radar waves off the asteroid, mapping its size and shape, and hopefully obtain some very high-resolution images.

“Using the Goldstone radar operating with the software and hardware upgrades, the resulting images of YU55 could come in with resolution as fine as 4 meters per pixel. We’re talking about getting down to the kind of surface detail you dream of when you have a spacecraft fly by one of these targets.”

– Lance Benner, JPL radio astronomer

Even though YU55 will remain at a safe distance the event is still quite notable. The last time an object this large came so close to Earth was in 1976… and scientists weren’t even aware of it at the time. Luckily we now have programs like the Near-Earth Objects Observations Program – a.k.a. “Spaceguard” –  to identify asteroids like this, hopefully in time to know if they could become a danger to our planet in either the near or distant future.

As of now, no large space rock with Earth’s name on it has been positively identified… but that doesn’t mean there’s nothing out there either. We need to keep diligent, keep looking and, above all, keep funding programs like this. If anything, this pass should serve as a reminder – however harmless – that we certainly are not alone in the solar system!

Read more on the NASA/JPL press release here.

UPDATE: NASA will be holding a live Q&A on 2005 YU55 and other near-Earth objects on November 1 at 2:30 p.m. PDT (5:30 p.m. EDT)… watch live here.

 

 

Hello, Helene!

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On June 18, 2011, the Cassini spacecraft performed a flyby of Saturn’s moon Helene. Passing at a distance of 6,968 km (4,330 miles) it was Cassini’s second-closest flyby of the icy little moon.

The image above is a color composite made from raw images taken with Cassini’s red, green and blue visible light filters. There’s a bit of a blur because the moon shifted position in the frames slightly between images, but I think it captures some of the subtle color variations of lighting and surface composition very nicely!

3D anaglyph of Helene assembled by Patrick Rutherford.

At right is a 3D anaglyph view of Helene made by Patrick Rutherford from Cassini’s original raw images … if you have a pair of red/blue glasses, check it out!

Cassini passed from Helene’s night side to its sunlit side. This flyby will enable scientists to create a map of Helene so they can better understand the moon’s history and gully-like features seen on previous flybys.

(When Cassini acquired the images, it was oriented such that Helene’s north pole was facing downwards. I rotated the image above to reflect north as up.)

Helene orbits Saturn at the considerable distance of 234,505 miles (377,400 km). Irregularly-shaped, it measures 22 x 19 x 18.6 miles (36 x 32 x 30 km).

Helene is a “Trojan” moon of the much larger Dione – so called because it orbits Saturn within the path of Dione, 60º ahead of it. (Its little sister Trojan, 3-mile-wide Polydeuces, trails Dione at the rear 60º mark.) The Homeric term comes from the behavioral resemblance to the Trojan asteroids which orbit the Sun within Jupiter’s path…again, 60º in front and behind. These orbital positions are known as Lagrangian points (L4 and L5, respectively.)

Read more on the Cassini mission site here.

An irregular crescent: Cassini's flyby of Helene on June 18, 2011.

Images: NASA / JPL / Space Science Institute.

Deep Impact

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Deep Impact is the name of a NASA space mission whose primary objective was to study Comet Tempel 1 (a.k.a. 9P/Tempel). It was launched on 12 January, 2005, and the smart impactor crashed into the comet on 4 July, 2005.

Oh, and yes, Deep Impact is also the name of a movie … but the two have no connection (the science team came up with their name independently of the Hollywood studio), other than that they both concern a comet!

Comets had been the focus of several space probes before Deep Impact, perhaps the most famous of which is the ESA’s Giotto flyby of Comet Halley. However, flybys could not, and cannot, tell us much about what’s beneath the cometary surface; in particular, what the relative amounts of ices and dust is, how porous the comet body is, and so on. The Deep Impact mission was designed to address many of these unknowns.

The space probe consisted of two parts, a 370 kg copper Smart Impactor – that smashed into the comet – and the Flyby section, which watched the impact from a safe distance. In addition, many ground-based telescopes – including those of thousands of amateurs – and some space-based ones, watched the event from an even safer distance.

The mission was a great success in that the heavy copper section did, in fact, smash into the comet, and the other section did observe the impact up-close-and-personal, but safely. A great deal was learned about this comet – its composition and mechanical strength, etc – and comets in general. However, the plume which resulted from the impact was much denser than expected, so the Flyby did not get any images of the impact crater itself.

After the encounter with Comet Tempel 1, an extended mission for the Flyby was designed and implemented, called EPOXI, after its two objectives: the Extrasolar Planet Observation and Characterization (EPOCh) and the Deep Impact Extended Investigation (DIXI) … hence Extrasolar Planet Observation and Deep Impact Extended Investigation. The former uses the larger telescope on the space probe to look for exoplanet transits; the latter is a flyby of another comet, Hartley 2, now expected on 11 October, 2010.

There are several official Deep Impact websites, including NASA’s, JPL’s (Jet Propulsion Laboratory), and the University of Maryland’s on EPOXI.

The Deep Impact mission resulted in lots of Universe Today stories, far too many to mention here. Some of the best are Deep Impact Smashes into Temple 1, What the Ground Telescopes Saw During Deep Impact, Deep Impact Turns Up Cometary Ice, and Deep Impact Begins Searching for Extrasolar Planets.

Comets, our Icy Friends from the Outer Solar System is a good Astronomy Cast episode which gives a good background on comets.

Source: NASA