Category Archives: Comets and Asteroids
Remember that comet-no-wait-asteroid astronomers discovered in October on a high-velocity hyperbolic orbit around the Sun? It has been determined that the object must be of interstellar origin and, based on follow-up observations over the past several weeks, it’s shaped like nothing that’s ever been seen before.
“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.
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.
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.
This is our best look yet at asteroid 2014 JO25, which made its closest pass by Earth for at least the next 500 years on April 19, 2017. The animation above is composed of radar observations made from NASA’s Goldstone facility in California when the asteroid was between 1.53 and 1.61 million miles away. These and earlier, lower-resolution images obtained the previous day (you can see those here) showed this asteroid to be a contact binary—two objects connected by a “neck” of material, not unlike the comet 67P that ESA’s Rosetta mission explored. The largest section of JO25 is estimated to be 2,000 feet (610 meters) wide, and at its widest the entire asteroid is about 3,300 feet (1 km) across. Observations also show JO25 rotates once every 4.5 hours.