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We May Have Just Been Visited By An Interstellar Comet

“This object came from outside our solar system.”
— Rob Weryk, postdoctoral researcher at University of Hawaii’s Institute for Astronomy

Diagram of the path of C/2017 U1 PanSTARRS (now A/2017 U1), a possible interstellar comet (or asteroid) spotted on Oct. 18, 2017. (NASA/JPL)

On October 14, 2017, what appears to be a comet (er, make that asteroid…read more below) sped past Earth at a distance of about 15 million miles after swinging around the Sun. It had come within 23.4 million miles of our home star over a month earlier on Sept. 9, and in fact wasn’t spotted by astronomers until Oct. 18—four days after its closest pass by us.

Further observations showed that the approximately 525-foot-wide object (an estimate based on its reflectivity) first approached traveling 16 miles a second from the direction of the constellation Lyra—quite a high angle from the plane of the rest of the Solar System—and is on a hyperbolic trajectory, moving quickly enough both in- and outbound along its course to permanently escape the Sun’s gravity unlike any other comet asteroid ever observed.

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OSIRIS-REx Sees the Moon Like We Can’t

The Moon imaged by OSIRIS-REx on Sept. 25, 2017. Credit: NASA/Goddard/University of Arizona.

On September 22 NASA’s OSIRIS-REx spacecraft made a “slingshot” gravity-assist pass by Earth in order to adjust the angle of its flight toward Bennu. Mission scientists took the opportunity to test out the spacecraft’s cameras with planned observations of Earth and the Moon, and I’m happy to report that everything worked out perfectly! Some of the first images shared with the public were of Earth from a distance of 106,000 miles; this one shows the Moon imaged from 746,000 miles away three days later on Sept. 25. It’s literally a view of the Moon we can’t ever get from Earth!

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Just Passing By: the Globe of Earth Imaged by OSIRIS-REx

Earth imaged on Sept. 22, 2017 by the MapCam instrument aboard OSIRIS-REx. Credit: NASA/Goddard/University of Arizona

Here’s our beautiful blue marble as seen by NASA’s OSIRIS-REx spacecraft on Sept. 22, 2017 from a distance of 106,000 miles (170,000 km). It had just completed a gravity-assist flyby of Earth—a little 19,000 mph “once around the block” that gave the spacecraft an 8,500-mile-an-hour speed boost necessary to adjust its course toward Bennu, the asteroid target of its mission.

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Spacecraft Down: Cassini is Gone


It’s official: Cassini’s mission at Saturn is over. Today, at 6:31 a.m. EDT (10:31 UTC), Cassini entered the atmosphere of Saturn. A little over a minute later it sent its final transmission back to Earth before succumbing to the physical forces of entry. That signal, Cassini’s last piece of data, ended at 7:55 a.m. EDT (11:55 UTC). After over thirteen years in orbit Cassini is now a part of Saturn; its work is done.

Mission accomplished.

About 14 hours earlier Cassini transmitted its final images of Saturn to Earth. You can see some of those below: Read the rest of this entry

It’s Time to Say Goodbye to Cassini

Artist’s rendering of Cassini at Saturn. Credit: NASA/JPL

Well, the day has come. Today is the last full day that NASA’s Cassini spacecraft will exist, and in fact right now it is on its final path—a grand soaring arc that will send it down into the atmosphere of Saturn itself on the morning of Friday, Sept. 15. It will be the closest to the ringed planet any spacecraft will have ever gotten, but it’s a trip that Cassini will not long survive. It’s the long-planned end of a glorious mission of exploration and discovery—not to mention beauty, art, and inspiration—and while Cassini itself will soon be gone, the enormous amount of data it has gathered in the twenty years since its launch will continue to drive discovery for many, many years to come.

(At least that’s what we’re all telling ourselves to make the loss a bit easier to bear.)

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