Planetary Defense: Tonight begin the Bennu Experiment

NASA – OSIRIS-REx Mission patch.

Dec. 31, 2018

On Dec. 3, after traveling billions of kilometers from Earth, NASA’s OSIRIS-REx spacecraft reached its target, Bennu, and kicked off a nearly two-year, up-close investigation of the asteroid. It will inspect nearly every square inch of this ancient clump of rubble left over from the formation of our solar system. Ultimately, the spacecraft will pick up a sample of pebbles and dust from Bennu’s surface and deliver it to Earth in 2023.

Image above: This artist’s concept shows the Origins Spectral Interpretation Resource Identification Security – Regolith Explorer (OSIRIS-REx) spacecraft contacting the asteroid Bennu with the Touch-And-Go Sample Arm Mechanism or TAGSAM. The mission aims to return a sample of Bennu’s surface coating to Earth for study as well as return detailed information about the asteroid and it’s trajectory. Image Credits: NASA’s Goddard Space Flight Center.

The spacecraft’s first orbital insertion is scheduled for Dec. 31 (today), and OSIRIS-REx will remain in orbit until mid-February 2019, when it exits to initiate another series of flybys for the next survey phase. During the first orbital phase, the spacecraft will orbit the asteroid at a range of 0.9 miles (1.4 km) to 1.24 miles (2.0 km) from the center of Bennu — setting new records for the smallest body ever orbited by a spacecraft and the closest orbit of a planetary body by any spacecraft.

Generations of planetary scientists will get to study pieces of the primitive materials that formed our cosmic neighborhood and to better understand the role asteroids may have played in delivering life-forming compounds to planets and moons.

But it’s not just history that the mission to Bennu will help uncover. Scientists studying the rock through OSIRIS-REx’s instruments in space will also shape our future. As they collect the most detailed information yet about the forces that move asteroids, experts from NASA’s Planetary Defense Coordination Office, who are responsible for detecting potentially hazardous asteroids, will improve their predictions of which ones could be on a crash-course with our planet.

Here is how the OSIRIS-REx mission will support this work:

How scientists predict Bennu’s whereabouts

About a third of a mile, or half a kilometer, wide, Bennu is large enough to reach Earth’s surface; many smaller space objects, in contrast, burn up in our atmosphere. If it impacted Earth, Bennu would cause widespread damage. Asteroid experts at the Center for Near-Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory in Pasadena, California, project that Bennu will come close enough to Earth over the next century to pose a 1 in 2,700 chance of impacting it between 2175 and 2196. Put another way, those odds mean there is a 99.963 percent chance the asteroid will miss the Earth. Even so, astronomers want to know exactly where Bennu is located at all times.

Animation above: This series of images taken by the OSIRIS-REx spacecraft shows Bennu in one full rotation from a distance of around 50 miles (80 km). The spacecraft’s PolyCam camera obtained the thirty-six 2.2-millisecond frames over a period of four hours and 18 minutes. Animation Credits: NASA’s Goddard Space Flight Center/University of Arizona.

Astronomers have estimated Bennu’s future trajectory after observing it several times since it was discovered in 1999. They’ve turned their optical, infrared and radio telescopes toward the asteroid every time it came close enough to Earth, about every six years, to deduce features such as its shape, rotation rate and trajectory.

“We know within a few kilometers where Bennu is right now,” said Steven Chesley, senior research scientist at CNEOSand an OSIRIS-REx team member whose job it is to predict Bennu’s future trajectory.

Why Bennu’s future trajectory predictions get fuzzy

Scientists have estimated Bennu’s trajectory around the Sun far into the future. Their predictions are informed by ground observations and mathematical calculations that account for the gravitational nudging of Bennu by the Sun, the Moon, planets and other asteroids, plus non-gravitational factors.

Given these parameters, astronomers can predict the next four exact dates (in September of 2054, 2060, 2080 and 2135) that Bennu will come within 7.5 million kilometers (5 million miles or .05 astronomical units) of Earth. That’s close enough that Earth’s gravity will slightly bend Bennu’s orbital path as it passes by. As a result, the uncertainty about where the asteroid will be each time it loops back around the Sun will grow, causing predictions about Bennu’s future orbit to become increasingly hazy after 2060.

In 2060, Bennu will pass Earth at about twice the distance from here to the Moon. But it could pass at any point in a 30-kilometer (19-mile) window of space. A very small difference in position within that window will get magnified enormously in future orbits and make it increasingly hard to predict Bennu’s trajectory.

As a result, when this asteroid comes back near Earth in 2080, according to Chesley’s calculations, the best window we can get on its whereabouts is 14,000 kilometers (nearly 9,000 miles) wide. By 2135, when Bennu’s shifted orbit is expected to bring it closer than the Moon, its flyby window grows wider, to 160,000 kilometers (nearly 100,000 miles). This will be Bennu’s closest approach to Earth over the five centuries for which we have reliable calculations.

“Right now, Bennu has the best orbit of any asteroid in our database,” Chesley said. “And yet, after that encounter in 2135, we really can’t say exactly where it is headed.”

Animation above: This picture shows the OSIRIS-REx spacecraft’s view of Bennu during the final phase of its journey to the asteroid. From Aug. 17 through Nov. 27 the spacecraft’s PolyCam camera imaged Bennu almost daily as the spacecraft traveled 1.4 million miles (2.2 million km) toward the asteroid. The final images were obtained from a distance of around 40 miles (65 km). During this period, OSIRIS-REx completed four maneuvers slowing the spacecraft’s velocity from approximately 1,100 mph (491 m/sec) to 0.10 mph (0.04 m/sec) relative to Bennu, which resulted in the slower approach speed at the end of the video. Animation Credits: NASA’s Goddard Space Flight Center/University of Arizona.

There’s another phenomenon nudging Bennu’s orbit and muddying future impact projections. It’s called the Yarkovsky effect. Having nothing to do with gravity, the Yarkovsky effect sways Bennu’s orbit because of heat from the Sun.

“There are a lot of factors that might affect the predictability of Bennu’s trajectory in the future, but most of them are relatively small,” says William Bottke, an asteroid expert at the Southwest Research Institute in Boulder, Colorado, and a participating scientist on the OSIRIS-REx mission. “The one that’s most sizeable is Yarkvovsky.”

This heat nudge was named after the Polish civil engineer who first described it in 1901: Ivan Osipovich Yarkovsky. He suggested thatsunlight warms one side of a small, dark asteroid and some hours later the heat radiates away as the asteroid rotates its hot side into cold darkness. This thrusts the rock pile a bit, either toward the Sun or away from it, depending on the direction of its rotation.

In Bennu’s case, astronomers have calculated that the Yarkovsky effect has shifted its orbit about 284 meters (0.18 miles) per year toward the Sunsince 1999. In fact, it helped deliver Bennu to our part of the solar system, in the first place, from the asteroid belt between Mars and Jupiter over billions of years. Now, Yarkovsky is complicating our efforts to make predictions about Bennu’s path relative to Earth.

Getting face-to-face with the asteroid will help

The OSIRIS-REx spacecraft will use its suite of instruments to transmit radio tracking signals and capture optical images of Bennu that will help NASA scientists determine its precise position in the solar system and its exact orbital path. Combined with existing, ground-based observations, the space measurements will help clarify how Bennu’s orbit is changing over time.

Additionally, astronomers will get to test their understanding of the Yarkovksy effect on a real-life asteroid for the first time. They will instruct the spacecraft to follow Bennu in its orbit about the Sun for about two years to see whether it’s moving along an expected path based on gravity and Yarkovsky theories. Any differences between the predictions and reality could be used to refine models of the Yarkovsky effect.

But even more significant to understanding Yarkovsky better will be the thermal measurements of Bennu. During its mission, OSIRIS-REx will track how much solar heat radiates off the asteroid, and where on the surface it’s coming from—data that will help confirm and refine calculations of the Yarkovsky effect on asteroids.

The spacecraft also will address some open questions about the Yarkovsky theory. One of them, said Chesley, is how do boulders and craters on the surface of an asteroid change the way photons scatter off of it as it cools, carrying away momentum from the hotter side and thereby nudging the asteroid in the opposite direction? OSIRIS-REx will help scientists understand by mapping the rockiness of Bennu’s surface.

“We know surface roughness is going to affect the Yarkovsky effect; we have models” said Chesley. “But the models are speculative. No one has been able to test them.”

After the OSIRIS-REx mission, Chesley said, NASA’s trajectory projections for Bennu will be about 60 times better than they are now.

Related article:

NASA’s Newly Arrived OSIRIS-REx Spacecraft Already Discovers Water on Asteroid
http://orbiterchspacenews.blogspot.com/2018/12/nasas-newly-arrived-osiris-rex.html

Related links:

Center for Near-Earth Object Studies (CNEOS): https://cneos.jpl.nasa.gov/

OSIRIS-REx (Origins Spectral Interpretation Resource Identification Security Regolith Explorer): http://www.nasa.gov/mission_pages/osiris-rex/index.html

Image (mentioned), Animations (mentioned), Text, Credits: NASA/Dwayne Brown/JoAnna Wendel/Tricia Talbert/JPL/DC Agle/Goddard Space Flight Center, by Lonnie Shekhtman.

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Hubble Paved the Way for the New Horizons Mission to Pluto and Ultima Thule

NASA –  New Horizons Mission patch.

December 31, 2018

New Year’s Ultima Thule encounter

Years before a team of researchers proposed a mission called New Horizons to explore the dwarf planet Pluto, NASA’s Hubble Space Telescope had already made initial observations of the world at the dim outer fringes of our celestial neighborhood. Over many years, Hubble’s pioneering observations repeatedly accomplished what ground-based telescopes could not — imaging features on Pluto’s surface, finding new Plutonian moons, and tracking down a destination to visit after Pluto — an even tinier, icy object in a vast region of small worlds beyond the orbit of Neptune called the Kuiper Belt.

Image above: NASA’s Hubble Space Telescope has explored the universe since the early 1990s, gathering visible, near-ultraviolet, and near-infrared imagery and spectra. From its location in space, the telescope avoids the distortion produced by Earth’s atmosphere, enabling it to take images in higher resolutions at greater distances than possible with ground-based telescopes. Image Credit: NASA.

Thus began a decades-long relationship between Hubble and NASA’s New Horizons mission: A legendary space-based telescope and a pioneering space probe hurtling through space at about 32,000 miles (51,500 kilometers) per hour.

In 1990, Hubble produced the first image that illuminated Pluto and its large moon Charon. After Hubble’s optical repair in 1993, scientists captured even sharper images. New Horizons Principal Investigator Alan Stern of the Southwest Research Institute in Boulder, Colorado, led the imaging projects while co-investigator Marc Buie, now at SwRI Boulder but then at Lowell Observatory where Pluto was discovered, led the data analysis.

Where is New Horizons? Image Credit: JHUAPL

“We got eight pixels of Pluto in 1994. Each pixel represented more than 150 square miles of Pluto’s surface. Fast forward to 2002 and we got even fewer pixels per image. We had to wring every bit of information from each pixel possible,” Buie said. “It was a time- and computer-intensive process, but we were able to create the first maps of Pluto’s surface, and they were truly spectacular for their time.”

Those crude but valuable maps provided the best evidence that Pluto was not simply a homogenous ball of ices, but has a complex, variegated surface — a promising aspect for close-up inspection by a visiting spacecraft. Hubble’s cameras revealed nearly a dozen distinctive bright features, none of which had ever been seen before, including a “ragged” northern polar cap bisected by a dark strip, a puzzling high-contrast bright spot seen rotating with the planet, a cluster of dark spots, and a bright linear marking. That bright spot feature, unusually rich in carbon monoxide frost, became the prime target for New Horizons to examine up close after NASA funded the mission in 2002.

Image above: This is the first detection of Ultima Thule using the highest resolution mode of the Long Range Reconnaissance Imager (LORRI) aboard the New Horizons spacecraft. Three separate images, each with an exposure time of 0.5 seconds, were combined to produce the image. All three images were taken on Dec. 24, when Ultima was 4 billion miles (6.5 billion kilometers) from the Sun and 6.3 million miles (10 million kilometers) from the New Horizons spacecraft.(Click for full caption). Image Credits: NASA/JHUAPL/SwRI.

Although Charon was discovered in 1978 using ground-based telescopes, Hubble detected all four of Pluto’s other moons: Nix and Hydra in 2005, Kerberos in 2011, and Styx in 2012. These moons were spotted in the Hubble images by New Horizons team members, most notably Project Scientist Hal Weaver of the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, and co-investigator Mark Showalter of the SETI Institute in Mountain View, California. By the time the latter two moons were discovered, New Horizons was in the final years of its almost decade-long, 3-billion-mile sprint from Earth to Pluto.

Image above: Illustration of NASA’s New Horizons spacecraft encountering 2014 MU69 – nicknamed “Ultima Thule” – a Kuiper Belt object that orbits one billion miles beyond Pluto. Set for New Year’s 2019, New Horizons’ exploration of Ultima will be the farthest space probe flyby in history. Image Credits: NASA/JHUAPL/SwRI.

The discovery of these four small satellites was critical to overall Pluto flyby planning by identifying potential hazards, verifying the optimal spacecraft trajectory, and establishing the need for time to include observations of them as part of the flyby observing sequence. Without Hubble, New Horizons would have discovered these moons only a few months before the encounter — too late to effectively plan for their detailed study. To examine the possibility for an extended mission into the Kuiper Belt, the New Horizons team used Hubble in 2014 to conduct a needle-in-a-haystack search for a suitable Kuiper Belt Object that New Horizons could visit after passing Pluto. Hubble’s sensitive telescope allowed it to look for fainter KBOs than ground-based telescopes can see. Hubble took deep exposures on 20 areas of the sky and found three suitable KBO targets about one billion miles beyond Pluto. Following NASA approval for a mission extension in 2016, Stern selected 2014 MU69, since nicknamed Ultima Thule, as the target for its January 2019 flyby. In the years since, Hubble has measured the target’s red color and refined its orbit with dozens of additional observations.

Image above: NASA’s Hubble Space Telescope discovered the next target for the New Horizons spacecraft — 2014 MU69, nicknamed Ultima Thule — in June 2014. Seen in these five overlaid images, the object resides more than one billion miles beyond Pluto in the frigid outer reaches of the Kuiper Belt. New Horizons will reach Ultima Thule on New Year’s Day 2019. Image Credits: NASA/STScI/JHUAPL/SwRI.

“Without Hubble there would be no flyby of Ultima Thule,” said Stern. “And without Hubble, New Horizons would not have been as productive studying Pluto’s small moons. In fact, without Hubble’s early images revealing how interesting Pluto’s surface markings are, there might have never been a mission to explore this fascinating dwarf planet.”

New Horizons Beyond Pluto

The New Horizons spacecraft is now on course to fly by Ultima Thule — the farthest object ever explored by humankind — on New Year’s Day, Jan. 1, at 12:33 a.m. EST. Follow New Horizons to Ultima Thule at http://pluto.jhuapl.edu/Mission/Where-is-New-Horizons.php.

For more information on the New Horizons mission, including fact sheets, schedules, video and images, visit: https://www.nasa.gov/newhorizons

Images (mentioned), Video, Text, Credits: NASA/JHUAPL.

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An exoplanet covered with sapphires and rubies discovered by scientists

University of Zurich logo / University of Cambridge logo.

Dec. 31, 2018

Image above: Illustration of one of the exotic planets, rich in sapphires and rubies, observed by Zurich and British researchers. – Thibaut Roger / University of Zurich UZH.

Scientists think they have discovered a new type of exoplanet. A team of researchers from the Universities of Zurich (Switzerland) and Cambridge (United Kingdom) has unearthed an extrasolar planet called HD219134b with a surface covered with sapphires and rubies.

This exoplanet is located in the constellation Cassiopeia, 21 light years from Earth. It is five times heavier than the Earth because it consists of a heart rich in calcium and aluminum.

Planets that shine

The planet HD219134 b has a high temperature because it is very close to its star. According to the first observations of the scientists, this temperature could be at the origin of the chemical reactions which caused the creation of the ruby ​​blocks.

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“Maybe it shines with a blue and a red like rubies and sapphires, because these precious stones are aluminum oxides, common on this exoplanet”, explains Caroline Dion, astrophysicist at the university from Zurich. According to her, this type of planet could be more common than we think, favoring the creation of a new category of exotic and rocky super-lands.

University of Zurich (UZH): https://www.uzh.ch/en.html

University of Cambridge: https://www.cam.ac.uk/

Images, Text, Credits: ATS / UZH / Orbiter.ch Aerospace / Roland Berga.

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