The Interstellar Comet Has Arrived in Time for the Holidays

It got here out of the Northern sky, a frozen breath of fuel and dirt from the genesis of some distant star, launched throughout the galaxy by the gravitational maelstroms that accompany the beginning of worlds.

It wandered within the deep freeze of interstellar area for 100 million years or so, a locked vault of cosmo-chemical historical past. In Spring 2019 this ice dice started falling into our personal photo voltaic system. Feeble warmth from the solar, nonetheless distant, loosened carbon monoxide from its floor right into a faint, glowing fog; the orphan ice dice turned a brand new comet.

Six months later, Gennady Borisov, a Crimean astronomer, noticed it drifting in entrance of the constellation Most cancers and sounded the alarm.

On Sunday, Dec. eight the comet that now bears his title — 2I Borisov — will make a large flip across the solar and started heading again out of the photo voltaic system. Because it departs, it should steadily brighten and develop in dimension as daylight continues to shake off the mud from an extended, chilly sleep. On Dec. 28 the comet will go 180 million miles from Earth, its closest strategy to our planet.

This procession is being greeted with hungry eyes by a species solely simply knocking on the door of interstellar exploration and longing for information from on the market.

“I think the sense of excitement stems in part from the timing of these discoveries,” Dr. Laughlin said. Oumuamua and Borisov, he added, augur well for a new telescope the National Science Foundation is building in Chile called the Large Synoptic Survey Telescope, which will sweep the entire sky every few days, producing in effect a movie of the universe.

That telescope will be superbly positioned to find more interloper comets, perhaps even in time to send probes to greet them with Deep Impact-style missions. “The situation is reminiscent of when the first transiting exoplanets were detected,” Dr. Laughlin said.

That discovery occurred in 1995, shortly before the Spitzer Space Telescope, which was built without exoplanets in mind, was launched.

Astronomers have long suspected that if anything came calling from another star system, it would be comets. New stars and planetary systems are surrounded by vast clouds of icy leftover fragments, so the story goes. These snowballs are easily dislodged by passing stars and knocked hither and fro — many inward toward their mother star and its planets, but others outward across the galaxy.

Until now, astronomers have lacked telescopes big and sensitive enough to detect them. Now, with telescopes like the Large Synoptic Survey Telescope and the Pan-STARRS in Hawaii, which discovered Oumuamua, they do.

Thus far, the two examples of interstellar comets that humans have observed could not be more different. Oumuamua was mistaken for an asteroid at first because it had no cometary cloud of gas and dust around it, at least that could be seen. But as it was traveling out of sight, small perturbations in its motion suggested that in fact the rock was actually a comet, being pushed around by jets of gas shooting from its surface.

Estimates of the object’s shape — long and cigarlike — spurred speculation that it could be an alien probe or even a solar sail. Recent analysis by Sergey Mashchenko, an astrophysicist at McMaster University in Ontario, has concluded that Oumuamua was less a rod than a thin slab rocking back and forth as sunlight and radiation wore it away.

“It was vanishing as it went away, like a bar of soap in the shower,” Dr. Laughlin said.

Borisov, in contrast, is thriving, sprouting a typically bushy, radiant tail. As a comet, it would be utterly ordinary if not for its origin. “Nothing about Borisov is weird,” Dr. Laughlin said. “With Oumuamua, everything was weird.”

Borisov looked like a comet from the start, enveloped in a cloud of gas, which is what enabled Mr. Borisov to recognize it so quickly. And everything the visitor has done since then has suggested that at least some comets out there are more or less like our neighborhood comets.

Mr. Borisov’s comet underwent an astronomical rite of passage of sorts in October, when the Hubble Space Telescope got a good look at it: a white knuckle at the head of a bluish fan of light.

Subsequent observations by telescopes on Earth have confirmed the presence of alien water and carbon monoxide as well as a growing list chemicals from another part of the universe. As of Nov. 24, the comet’s tail had grown to 100,000 miles long. The comet’s nucleus is only a mile across.

Early in November, the Gemini observatory spotted the wanderer passing about a billion light-years in front of a spiral galaxy “romantically known” as 2dFgrS TGN363Z174, said Travis Rector, an astronomer from the University of Alaska Anchorage who was involved in taking the photograph. As if to tease us humans with a reminder of places unknown and unvisitable, the backdrop to the portrait is speckled with faint smudges of even more distant galaxies and stars.

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