"The data rate is painfully slow from so far away," said Will Grundy of Lowell Observatory in Flagstaff, Arizona, one of the lead authors.

Astronomers reported Thursday that this pristine, primordial cosmic body now called Arrokoth — the most distant object ever explored — is relatively smooth with far fewer craters than expected. It's also entirely ultrared, or highly reflective, which is commonplace in the faraway Twilight Zone of our solar system known as the the Kuiper Belt.

Grundy said in an email that to the human eye, Arrokoth would look less red and more dark brown, sort of like molasses. The reddish color is indicative of organic molecules.

While frozen methane is present, no water has yet been found on the body, which is an estimated 22 miles (36 kilometers) long tip to tip. At a news conference Thursday in Seattle, New Horizons' chief scientist Alan Stern of Southwest Research Institute said its size was roughly that of the city.

As for the snowman shape, it's not nearly as flat on the backside as previously thought. Neither the small nor big sphere is fully round, but far from the flatter pancake shape scientists reported a year ago. The research team likened the somewhat flattened spherical forms to the shape of M&Ms.

No rings or satellites have been found. The light cratering suggests Arrokoth dates back to the formation of the solar system 4.5 billion years ago. It likely was created by a slow, gentle merger between two separate objects that possibly were an orbiting pair. The resulting fused body is considered a contact binary.

This kind of slow-motion hookup likely arose from collapsing clouds in the solar nebula, as opposed to intense collisions theorized to form these planetesimals, or little orbiting bodies.

New Horizons flew past Arrokoth on Jan. 1, 2019, more than three years after the spacecraft visited Pluto. Originally nicknamed Ultima Thule, the object received its official name in November; Arrokoth means sky in the language of the Native American Powhatan people.

Launched in 2006, the spacecraft is now 316 million miles (509 million kilometers) beyond Arrokoth. The research team is looking for other potential targets to investigate. Powerful ground telescopes still under construction will help survey this part of the sky.

Emerging technology will enable scientists to develop a mission that could put a spacecraft in orbit around Pluto, 3 billion miles (5 billion kilometers) away, according to Stern. After a few years, that same spacecraft could be sent even deeper into the Kuiper Belt to check out other dwarf planets and objects, he said.

The New Horizons scientists reported their latest findings at the annual meeting of the American Association for the Advancement of Science, as well as in three separate papers in the journal Science.

David Jewitt of the University of California, Los Angeles, who was not involved in the studies, said a flyby mission like New Horizons, where encounters last just a few days, is hardly ideal.

“For future missions, we need to be able to send spacecraft to the Kuiper Belt and keep them there” in orbit around objects, Jewitt wrote in a companion piece in Science. That would allow “these intriguing bodies to be studied in stunning geological and geophysical detail," he noted.

Quelle: abcNews

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New Horizons spacecraft 'alters theory of planet formation'

Scientists say they have "decisively" overturned the prevailing theory for how planets in our Solar System formed.

The established view is that material violently crashed together to form ever larger clumps until they became worlds.

New results suggest the process was less catastrophic - with matter gently clumping together instead.

The study appears in Science journal and has been presented at the American Association for the Advancement of Science meeting in Seattle.

The study's lead researcher, Dr Alan Stern, said that the discovery was of "stupendous magnitude".

"There was the prevailing theory from the late 1960s of violent collisions and a more recent emerging theory of gentle accumulation. One is dust and the other is the only one standing. This rarely happens in planetary science, but today we have settled the matter," he told BBC News.

The claim arises from detailed study of an object in the outer reaches of the Solar System. Named Arrokoth, the object is more than six billion km from the Sun in a region called the Kuiper belt. It is a pristine remnant of planet formation in action as the Solar System emerged 4.6 billion years ago, with two bodies combining to form a larger one.

Scientists obtained high-resolution pictures of Arrokoth when Nasa's New Horizons spacecraft flew close to it just over a year ago. It gave scientists their first opportunity to test which of the two competing theories was correct: did the two components crash together or was there gentle contact?

The analysis by Dr Stern and his team could find no evidence of violent impact. The researchers found no stress fractures, nor was there any flattening, indicating that the objects were squashed together gently.

"This is completely decisive," said Dr Stern. "In one fell swoop, the flyby of Arrokoth was able to decide between the two theories."

Image copyrightLUND OBSERVATORY

He is bullish because these so-called Kuiper belt objects have largely remained the same since the formation of the Solar System. They are, in effect, perfectly preserved fossils from this distant time.

The newer gentle clumping theory was developed 15 years ago by Prof Anders Johansen at Lund Observatory in Sweden. At the time he was a young PhD student. The idea emerged from computer simulations.

After speaking to Dr Stern, I broke the news to Prof Johansen that his theory had been confirmed. There was a pause on the line before he replied that he "felt great".

He added: "It is a special moment. I remember when I was a PhD student and feeling very nervous about these new results because they were very different to the ones before. I was worried that there was an error in my code or that I had made a calculation error.

"And then when you see these results confirmed from actual observations it is a real relief."

Prof Johansen commemorated the occasion with a pizza and coke with his family.

Engineer Dr Maggie Aderin-Pocock, who co-presents the BBC's Sky at Night programme, cautioned against toppling a theory based on the observation of one object, but said that Dr Stern's interpretation "makes a lot of sense".

"It is nice to have this evidence because the crashing together theory was a nice theory, but there were some challenges to it. Why did the objects stick together and not bounce apart. There was a lot that didn't add up."

When Arrokoth was discovered six years ago, it was known only by its designation 2014 MU69. At the time of the New Horizons flyby, it had been given the informal name Ultima Thule. While that name came from a classical and medieval term for a far-off place at the borders of the known world, its use by Nazi occultists as the mythical homeland of the Aryan race caused controversy.

The official name Arrokoth is a Native American term meaning "sky" in the Powhatan/Algonquian language.

Quelle: BBC

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Discoveries at solar system’s distant frontier shed light on how planets form

Data from the encounter of NASA’s New Horizons spacecraft with a frozen reddish snowman-shaped object a billion miles beyond Pluto last year suggest the building blocks of planets may have formed less violently than many scientists expected, officials said Thursday.

When new New Horizons zipped past the distant world Jan. 1, 2019, the probe captured imagery that showed it was formed of two smooth connected lobes, both reddish in color with little sign of structural damage, cracks or other evidence of a violent collision.

The appearance led scientists to hypothesize that the two lobes likely formed near one another soon after the birth of the solar system 4.5 billion years ago, then merged together at a relatively slow relative velocity. Modeling of data gathered by New Horizons during last year’s New Year’s Day flyby has confirmed the low-speed merger hypothesis.

Named Arrokoth, the dual-lobe world measures about 22 miles (36 kilometers) long, 12 miles (20 kilometers) wide, and around 6 miles (10 kilometers) thick. Scientists have compared its shape to a partially flattened snowman.

Arrokoth orbits the sun once every 293 years, and is located some 4.1 billion miles (6.6 billion kilometers) from Earth in the Kuiper Belt, a ring of small, icy worlds beyond the orbit of Neptune.

The New Horizons published three papers in the journal Science this week discussing the latest findings.

“Arrokoth is the most distant, most primitive and most pristine object ever explored by spacecraft, so we knew it would have a unique story to tell,” said Alan Stern, principal investigator on the New Horizons mission from the Southwest Research Institute in Boulder, Colorado. “It’s teaching us how planetesimals formed, and we believe the result marks a significant advance in understanding overall planetesimal and planet formation.”

Scientists formally named the object Arrokoth in November after initially giving it the nickname Ultima Thule, a term in medieval mythology that meant “beyond the borders of the known world.” Although the name “Ultima Thule” is centuries old, Nazis used the term to refer to the mythological birthplace of the Aryan race, prompting protests from numerous members of the scientific community and beyond.

Arrokoth means “sky” in the Powhatan/Algonquian language. With consent from Powhatan Tribal elders and representatives, NASA’s New Horizons team proposed the new name to the International Astronomical Union, which oversees the formal naming of planetary objects and astronomical features.

Planetesimals are the building blocks of planets, many of which accreted into ever-larger clumps to create worlds like Earth. But some of the would-be planets stopped growing as other planet-forming materials coalesced elsewhere, leaving behind time capsules like Arrokoth ripe for research using modern spacecraft, instrumentation and computer modeling.

The results show the two pieces that formed Arrokoth formed close together, orbited one another, and then finally merged at a speed equivalent to a brisk walking pace.

That evidence suggests Arrokoth was created in a much less violent way than some scientists theorized.

“Just as fossils tell us how species evolved on Earth, planetesimals tell us how planets formed in space,” said William McKinnon, a New Horizons co-investigator from Washington University in St. Louis, and lead author of an Arrokoth formation paper in Science this week. “Arrokoth looks the way it does not because it formed through violent collisions, but in more of an intricate dance, in which its component objects slowly orbited each other before coming together.”

Scientists have come up with two major competing theories explaining planetesimal formation. One is called the cloud collapse model, and other is known as hierarchical accretion.

Data from the New Horizons mission supports the cloud collapse theory, indicating Arrokoth formed as solid particles in the primordial solar nebula gently collapsed onto one another under the tug of gravity. The competing theory of hierarchical accretion supposes that planetesimals collided with each other at high speed like billiard balls to accrete into larger bodies.

Visual evidence from the New Horizons flyby last year supports modeling suggesting the two lobes came together at slow speeds.

There is no sign of visible damage at the surface of Arrokoth, and both lobes appear the same color with the same mineral composition, suggesting they formed from the same type of material in the same region of the ancient solar system.

“Arrokoth has the physical features of a body that came together slowly, with ‘local’ materials in the solar nebula,” said Will Grundy, New Horizons composition theme team lead from Lowell Observatory in Flagstaff, Arizona, and the lead author of another Science paper. “An object like Arrokoth wouldn’t have formed, or look the way it does, in a more chaotic accretion environment.”

Scientists said the flattened shape of Arrokoth and close alignment of the equators and poles on each lobe also supports the conclusion that the two segments did not collide chaotically.

“All of the evidence we’ve found points to particle-cloud collapse models, and all but rule out hierarchical accretion for the formation mode of Arrokoth, and by inference, other planetesimals,” Stern said in a statement.

The new papers published in Science are follow-ups to a paper from May 2019 that laid out the New Horizons team’s initial conclusions from the Arrokoth flyby. The information released Thursday is based on 10 times as much data as the May 2019 report.

New Horizons flew by Arrokoth at a relative velocity of roughly 32,000 mph, or 9 miles per second (14 kilometers per second), obtaining a snapshot view the faraway world.

The fresh data downlinked New Horizons since last May also produced refined estimates of Arrokoth’s dimensions.

Scientists estimate Arrokoth’s larger lobe is about 12.8 miles (20.6 kilometers) by 12.4 miles (19.9 kilometers) by 5.8 miles (9.4 kilometers). The smaller lobe is roughly 9.6 miles (15.4 kilometers) by 8.6 miles (13.8 kilometers) by 6.1 miles (9.8 kilometers).

The updated dimensions give Arrokoth a volume about 30 percent larger than the previous estimate, the New Horizons team wrote in one of the Science papers this week.

Launched in 2006, the New Horizons spacecraft obtained the first up-close glimpse of Pluto and its moons in July 2015. Ground controllers steered the probe toward a second, more distant flyby target with leftover fuel after scientists discovered Arrokoth with the Hubble Space Telescope.

New Horizons is now in an extended mission, using its instruments to make long-range observations of other Kuiper Belt Objects and collect data on the radiation and dust environment more than 4 billion miles from the sun.

Scientists plan to use ground-based telescopes later this year to search for another target in the Kuiper Belt that New Horizons could reach for a close-up flyby in the coming years.

Quelle: SN

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Update: 13.06.2020

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NASA's New Horizons Conducts the First Interstellar Parallax Experiment

For the first time, a spacecraft has sent back pictures of the sky from so far away that some stars appear to be in different positions than we see from Earth.

More than four billion miles from home and speeding toward interstellar space, NASA's New Horizons has traveled so far that it now has a unique view of the nearest stars. "It's fair to say that New Horizons is looking at an alien sky, unlike what we see from Earth," said Alan Stern, New Horizons principal investigator from Southwest Research Institute (SwRI) in Boulder, Colorado. "And that has allowed us to do something that had never been accomplished before — to see the nearest stars visibly displaced on the sky from the positions we see them on Earth."

On April 22-23, the spacecraft turned its long-range telescopic camera to a pair of the closest stars, Proxima Centauri and Wolf 359, showing just how they appear in different places than we see from Earth. Scientists have long used this "parallax effect" – how a star appears to shift against its background when seen from different locations -- to measure distances to stars.

An easy way to see parallax is to place one finger at arm's length and watch it jump back and forth when you view it successively with each eye. Similarly, as Earth makes it way around the Sun, the stars shift their positions. But because even the nearest stars are hundreds of thousands of times farther away than the diameter of Earth's orbit, the parallax shifts are tiny, and can only be measured with precise instrumentation.

"No human eye can detect these shifts," Stern said.

But when New Horizons images are paired with pictures of the same stars taken on the same dates by telescopes on Earth, the parallax shift is instantly visible. The combination yields a 3D view of the stars "floating" in front of their background star fields.

"The New Horizons experiment provides the largest parallax baseline ever made -- over 4 billion miles -- and is the first demonstration of an easily observable stellar parallax," said Tod Lauer, New Horizons science team member from the National Science Foundation's National Optical-Infrared Astronomy Research Laboratory who coordinated the parallax demonstration.

New Horizons contributing scientist, astrophysicist and legendary Queen guitarist Brian May uses an OWL viewer to check out the stereo images of Proxima Centauri he created by combining pictures from Earth-based telescopes and the New Horizons spacecraft. (Photos courtesy of Brian May)

Working in Stereo

Lauer, New Horizons Deputy Project Scientist John Spencer, of SwRI, and science team collaborator, astrophysicist, Queen guitarist and stereo imaging enthusiast Brian May created the images that clearly show the effect of the vast distance between Earth and the two nearby stars.

"It could be argued that in astro-stereoscopy -- 3D images of astronomical objects – NASA's New Horizons team already leads the field, having delivered astounding stereoscopic images of both Pluto and the remote Kuiper Belt object Arrokoth," May said. "But the latest New Horizons stereoscopic experiment breaks all records. These photographs of Proxima Centauri and Wolf 359 – stars that are well-known to amateur astronomers and science fiction aficionados alike -- employ the largest distance between viewpoints ever achieved in 180 years of stereoscopy!"

The companion Earth-based images of Proxima Centauri and Wolf 359 were provided by the Las Cumbres Observatory, operating a remote telescope at Siding Spring Observatory in Australia, and astronomers John Kielkopf, University of Louisville, and Karen Collins, Harvard and Smithsonian Center for Astrophysics, operating a remote telescope at Mt. Lemmon Observatory in Arizona.

"The professional and amateur astronomy communities had been waiting to try this, and were very excited to make a little space exploration history," said Lauer. "The images collected on Earth when New Horizons was observing Proxima Centauri and Wolf 359 really exceeded my expectations."

An Interstellar Navigation First

Throughout history, navigators have used measurements of the stars to establish their position on Earth. Interstellar navigators can do the same to establish their position in the galaxy, using a technique that New Horizons has demonstrated for the first time. While radio tracking by NASA's Deep Space Network is far more accurate, its first use is a significant milestone in what may someday become human exploration of the galaxy.

At the time of the observations, New Horizons was more than 4.3 billion miles (about 7 billion kilometers) from Earth, where a radio signal, traveling at the speed of light, needed just under 6 hours and 30 minutes to reach home.

Launched in 2006, New Horizons is the first mission to Pluto and the Kuiper Belt. It explored Pluto and its moons in July 2015 -- completing the space-age reconnaissance of the planets that started 50 years earlier -- and continued on its unparalleled voyage of exploration with the close flyby of Kuiper Belt object Arrokoth in January 2019. New Horizons will eventually leave the solar system, joining the Voyagers and Pioneers on their paths to the stars.

Flicker

This two-frame animation blinks back and forth between New Horizons and Earth images of each star, clearly illustrating the different view of the sky New Horizons has from its deep-space perch.

Proxima Centauri

Wolf 359

Stereo for 3D Glasses

These anaglyph images can be viewed with red-blue stereo glasses to reveal the stars' distance from their backgrounds.

Proxima Centauri

Wolf 359

Parallel Stereo

Use a stereo viewer for these images; if you don't have a viewer, change your focus from the image by looking "through" it (and the screen) and into the distance. This creates the effect of a third image in the middle, and try setting your focus on that third image. The New Horizons image is on the left.

Proxima Centauri

Wolf 359

Cross-Eyed Stereo

For this view, cross your eyes until the pair of images merges into one. It might help to place your finger or a pen just a couple of inches from your eyes, and focus on it. When the background image comes into focus, remove the closer object and concentrate on the image.

Proxima Centauri

Wolf 359