Ultima Thule last: an ancient red world, lobe dancing to


An image of Ultima Thule taken by New Horizons on New Year's Day, 2019.

APL / SWRI from NASA / JHU / Thomas Appere

Scientists explain that details on the strange shape of a globe known as the Ultima Thule, at 6.5 billion kilometers, provide insight into the formation of the solar system.

When NASA's New Horizons spacecraft flew over on January 1, 2019, its first views of the Kuiper Belt object revealed something like a two-lobed snowman connected by a narrow neck .

But as later views showed from different angles, scientists realized that the two "balls" that made up the snowman were spheres, but were flattened and elongated – more like deformed biscuits or burgers than meatballs.

Now, the researchers say that it seems that they are also very precisely aligned with each other.

"The two lobes have axes: a long axis, a short axis and an intermediate axis," says William McKinnon of Washington University in St Louis, United States.

The researcher presented his findings at the 50th Annual Lunar and Planetary Science Conference, held this week in The Woodlands, Texas.

"It seems that these axes are remarkably well aligned, certainly at less than 10 degrees [of each other] and probably even better than that. It is highly unlikely that this will happen completely by chance. "

This unusual alignment, he says, indicates that the two bodies that merged to create Ultima Thule did not meet randomly.

Instead, they were orbiting one around the other with the tidal forces coming from their mutual gravitational pull, which led them to align one on the other. l & # 39; other. "[Then] they merge and stay on the main axis … end to end. "

Other evidence shows that when the two objects merged, they did it very gently. "You do not see signs of violence or stress fractures," said Alan Stern of the Southwest Research Institute (SWRI) of Boulder, Colorado, principal investigator of New Horizons.

McKinnon adds that the collision probably occurred at two meters per second, roughly the speed of a brisk walk.

All of this, he adds, supports a model of planet formation in which building blocks are formed from clusters of gravitational collapses of particles the size of a pebble, rather than what crashed, randomly.

"The evidence we have of Ultima Thule is that image and not the other," says McKinnon.

Stern adds, "It's a huge step forward."

Meanwhile, other scientists are studying other aspects of the world, seeking additional clues about its history.

Color images, for example, show that it is very red. According to Carly Howett, also from SWRI, it is likely that this is due to the effect of billions of years of sunlight on organic materials on the surface, which slowly converts them into a class of compounds sometimes called tholins.

"The coloring is consistent with the idea that we are looking at a primordial object," she says.

His SWRI colleague, Silvia Protopapa, adds that other spectroscopic features indicate that there is also water and methanol. The latter, she says, is also revealing of Ultima Thule's primordial nature.

"It's in comets and around protostars," she says.

Other details appear on the geology of the surface of the object. It has at least one large crater that appears to be an impact crater, as well as a chain of craters that could come from subsidence in an underground crack, says Kirby Runyon, a postdoctoral fellow at the Johns Hopkins Applied Physics Laboratory in the United States. .

There may also be sublimation hollows, formed when super-volatile compounds such as carbon monoxide burst from the subsoil, leaving crater-like imprints on the surface.

There are also hills, bumps, hollows and even signs of avalanches.

"Even if Earth's gravity is only 1: 100,000, things are always falling," says Runyon.

In addition, the neck between the two lobes seems folded on one side. "It may indicate the slow collision of these two lobes," says Runyon.

Stern adds that much more data is still ahead. "Most overflight data is still in the spacecraft," he says.

Once the rest of the data has been returned, towards the end of the summer of 2020, New Horizons will continue to study the interplanetary medium in the Kuiper Belt and adapt its onboard telescope to any object that is close enough to the Kuiper belt. To be visible.

But he also still has fuel for maneuvering, offering the prospect of another pass.

"We have more fuel on board than it took to target this overflight," Stern said.

There is only one problem: it was difficult enough to spot Ultima Thule from the Earth to be able to steer the spacecraft towards him.

"[And] As we get closer and closer, objects are getting weaker, as seen from Earth, "says Stern.

Most likely, he says, New Horizons will have to search for its next target with the help of its own telescope, hoping it detects something in time to reach it with the remaining fuel.

"We probably only have fuel for one," warns Stern, "[and] it may be necessary to be lucky to obtain it.

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