“This object came from outside our solar system.”
— Rob Weryk, postdoctoral researcher at University of Hawaii’s Institute for Astronomy
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.
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.)
Yes, it’s true. As of today, August 15, NASA’s Cassini spacecraft has less than 31 days—one full month—left in operation and, sadly, its existence. On September 15, 2017, Cassini will end its mission with a controlled dive into Saturn’s atmosphere…a journey that it will not long survive. But up until the very end Cassini, which has been exploring the majestic ringed planet and its family of moons since it arrived in the summer of 2004, will be making scientific observations and sending the data back to us here on Earth—at least as long as it possibly can. That data, in fact, will still be en route across the 900 million miles of space between us and Saturn for almost an hour after the spacecraft will have succumbed to the forces of atmospheric entry.
When Cassini’s final signal is received on Earth it will be a ghost message, sent from a ship that no longer exists.
Comets are the icy remnants left over from the formation of the Solar System. They circle the Sun in highly elliptical orbits that can range in length from several years to several million years, depending on their origin, and while they are usually quiet and dark when they get close enough to the Sun they are briefly heated enough to melt—technically sublimate—some of their frozen material, forming a cloud of gas and dust and a long tail sometimes big and bright enough to be visible from Earth.
But for the majority of their travels most comets are dark and difficult to spot, especially those originating from the Oort Cloud, an enormous spherical zone of icy debris surrounding our Solar System 186 billion miles away. Now, using infrared data from NASA’s WISE spacecraft, researchers have concluded that there are many more so-called “long period” comets visiting from the Oort Cloud than previously suspected—at least seven times more—and that they’re larger than we thought, too…many over half a mile across.
The end is near. On September 15, 2017, NASA’s Cassini spacecraft will end its mission as well as its very existence with a plunge into the atmosphere of the very planet it has been orbiting since June 2004. It’s a maneuver intended to protect the pristine environments of Saturn’s icy moons, some of which harbor hidden reserves of liquid water, from potential impact contamination by an incapacitated spacecraft at some distant time in the future. But even though the reasons are noble, there’s no doubt that the final flight of Cassini and its inevitable loss will be a sad event for all those — myself very much included — who have followed along on its journey of discovery all these years. (Literally my first feature post here was a picture from Cassini.)
The video above, released today by NASA, is a poignant look both back at Cassini’s voyages and ahead at its Grand Finale, the last and most daring part of its mission at Saturn. These last few months will be bittersweet for Cassini fans, as every week will bring us closer to the end but also new and breathtaking views of Saturn…up to and including one last “family portrait” of the planet, its beautiful rings, and family of amazing moons.
Must be dusty in here, there’s something in my eye…
The end phase of the mission begins April 22. Follow along with the Grand Finale here.