Earth Quasi Satellite (469219) 2016 HO3 an asteroid, not Space Junk

At the 49th Annual Division for Planetary Sciences Meeting in Provo, Utah, astronomers led by Vishnu Reddy at the University of Arizona confirm true nature of one of Earth's companions on its journey around the sun.  

Was it a burned-out rocket booster, tumbling along a peculiar near-earth orbit around the sun, and only occasionally getting close enough to be studied with even the largest telescopes?

Not at all, as it turns out. While, based on previous observations, most astronomers had strongly suspected that object (469219) 2016 HO3 was an ordinary asteroid and not space junk, it took a team of astronomers led by Vishnu Reddy, assistant professor at the Lunar and Planetary Laboratory, University of Arizona, working with one of the world’s largest telescopes, the Large Binocular Telescope (LBT), on Mt. Graham in Southeastern Arizona, to learn the true nature of this near-Earth object.

2016 HO3 is a small near-Earth object (NEO) measuring no more than 100 meters (330 feet) across that, while orbiting the Sun, also appears to circle around the Earth as a "quasi-satellite." Only five quasi-satellites have been discovered so far, but 2016 HO3 is the most stable of them. The provenance of this object is unknown. On timescales of a few centuries, 2016 HO3 remains within 38-100 lunar distances from us.

2016 HO3 is seen at the top left corner of this animation made of ten 2mn long exposures in I band using MODS1 on the left side of LBT - The telescope is tracking the moving asteroid, so background stars (and even a couple of galaxies) are trailed.  Credit LBTO

“While HO3 is close to the Earth, its small size – possibly not larger than 100 feet – makes it challenging target to study, said Reddy. “Our observations show that the HO3 rotates once every 28 minutes and is made of materials similar to asteroids." 

Soon after its discovery in 2016, astronomers were not sure where this object came from, but in a recent presentation at the annual Division for Planetary Sciences Conference of the American Astronomical Society in Provo, Utah, Reddy and his colleagues show that Earth’s new traveling buddy is an asteroid and not space junk. The new observations confirm that 2016 HO3 is a natural object of similar provenance to other small NEOs that zip by the Earth each month. 

"In an effort to constrain its rotation period and surface composition, we observed 2016 HO3 on April 14 and 18 with the Large Binocular Telescope and the Discovery Channel Telescope," Reddy said. "The derived rotation period and the spectrum of emitted light are not uncommon amongst small NEOs, suggesting that 2016 HO3 is a natural object of similar provenance to other small NEOs."

Light curve of 2016 HO3 showing the 28m rotation period of the asteroid
(MODS on LBT on Apr 14, and LMI on DCT on Apr 18)

In their presentation, "Ground-based Characterization of Earth Quasi Satellite (469219) 2016 HO3," Reddy and his co-authors, Olga Kuhn, Audrey Thirouin, Al Conrad, Renu Malhotra, Juan Sanchez, and Christian Veillet, point out that the light reflected off the surface of 2016 HO3 is similar to meteorites we have on Earth. 

One way to visualize HO3's orbit is by picturing a hula hoop dancer – the sun in this analogy – twirling two hoops around the hips at the same time, ever so slightly out of sync. While it orbits the sun, the object makes yearly loops (link to https://www.youtube.com/watch?v=zMJc7gmychk ) around the Earth. As a result, the object appears to orbit the Earth, but it is not gravitationally bound to our planet.

"Of the near-Earth objects we know of, these types of objects would be the easiest to reach, so they could potentially make suitable targets for exploration," said Veillet, director of the LBT Observatory. "With its binocular arrangement of two 8.4-meter mirrors, coupled with a very efficient pair of imagers and spectrographs like MODS, LBT is ideally suited to the characterization of these Earth's companions." 

NASA Near-Earth Object Observations Program Grant NNX17AJ19G (PI: Reddy) funded parts of this work. 

# # #
PIO Contact: Daniel W. Stolte +1 520-621-4402 stolte@email.arizona.edu
Science Contact at LPL: Vishnu Reddy reddy@lpl.arizona.edu
Science contact at LBTO: Christian Veillet cveillet@lbto.org

Reference:
"Ground-based Characterization of Earth Quasi Satellite (469219) 2016 HO3," Vishnu Reddy, Olga Kuhn, Audrey Thirouin, Al Conrad, Renu Malhotra, Juan A. Sanchez, Christian Veillet. 49th Annual Division for Planetary Sciences Meeting - Tuesday, October 17th, 2017. 204.07.

LBT snags first glimpse of OSIRIS-REx since launch

OSIRIS-REx is  a NASA spacecraft traveling to a near-Earth asteroid called Bennu to bring a small sample back to Earth for study. The mission launched Sept. 8, 2016, from Cape Canaveral Air Force Station. As planned, the spacecraft will reach Bennu in 2018 and return a sample to Earth in 2023.

The spacecraft is currently approaching Earth for its gravity assist maneuver, which will change its trajectory and set it on course to rendez-vous Bennu. Its closest approach to Earth is scheduled for 12:52 p.m. EDT on Friday, Sept. 22.

The Large Binocular Telescope Observatory (LBTO) used the LBCs (Large Binocular Cameras), a pair of wide-field cameras at the prime focus of each of its two 8.4m mirrors, to image the field around the predicted position of the spacecraft on the night of September 1.

The animation above (three images - LBCB - 300s exp. time - V filter) centered on OSIRIS-REx (red square).  2017 September 2 at around 11:00 UTC. The spacecraft was 11-million kilometers away from Earth at the time of the observation. The spacecraft was  28% illuminated with a magnitude V~25.

On that night, LBTO was back on sky after a long period of shutdown which started on June 15 due to the Frye fire, followed by its seasonal monsoon shutdown (Jul 10 - Aug 31). OSIRIS-REx was an excellent target of opportunity at the beginning of a 12-night period dedicated to a full restart of the facility. A good way to come back to observing after 2.5 months of closed dome!

Thanks go to V. Reddy and A. Conrad for proposing the target, B. Rothberg, O. Kuhn, J. Hill and S. Allanson for observing, C. Veillet and C. Hergenrother for the data reduction, and the whole LBTO staff for a great shutdown work!

The big star that couldn’t become a supernova

One star's "massive fail" could solve a mystery

OSU - For the first time in history, astronomers have been able to watch as a dying star was reborn as a black hole.

It went out with a whimper instead of a bang.

The star, which was 25 times as massive as our sun, should have exploded in a very bright supernova. Instead, it fizzled out—and then left behind a black hole.

“Massive fails” like this one in a nearby galaxy could explain why astronomers rarely see supernovae from the most massive stars, said Christopher Kochanek, professor of astronomy at The Ohio State University and the Ohio Eminent Scholar in Observational Cosmology.

As many as 30 percent of such stars, it seems, may quietly collapse into black holes—no supernova required.

“The typical view is that a star can form a black hole only after it goes supernova,” Kochanek explained. “If a star can fall short of a supernova and still make a black hole, that would help to explain why we don’t see supernovae from the most massive stars.”

He leads a team of astronomers who have been using the Large Binocular Telescope (LBT) to look for failed supernovae in other galaxies. They published their latest results in the Monthly Notices of the Royal Astronomical Society.

Among the galaxies they’ve been watching is NGC 6946, a spiral galaxy 22 million light-years away that is nicknamed the “Fireworks Galaxy” because supernovae frequently happen there. Starting in 2009, one particular star, named N6946-BH1, began to brighten weakly. By 2015, it appeared to have winked out of existence.

It’s too early in the project to know for sure how often stars experience massive fails, but Scott Adams, a former Ohio State student who recently earned his Ph.D. doing this work, was able to make a preliminary estimate.

“N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we’ve been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae,” he said.

He leads a team of astronomers who have been using the Large Binocular Telescope (LBT) to look for failed supernovae in other galaxies. They published their latest results in the Monthly Notices of the Royal Astronomical Society.

Among the galaxies they’ve been watching is NGC 6946, a spiral galaxy 22 million light-years away that is nicknamed the “Fireworks Galaxy” because supernovae frequently happen there. Starting in 2009, one particular star, named N6946-BH1, began to brighten weakly. By 2015, it appeared to have winked out of existence.

The astronomers aimed the Hubble Space Telescope at the star’s location to see if it was still there but merely dimmed. They also used the Spitzer Space Telescope to search for any infrared radiation emanating from the spot. That would have been a sign that the star was still present, but perhaps just hidden behind a dust cloud.

All the tests came up negative. The star was no longer there. By a careful process of elimination, the researchers eventually concluded that the star must have become a black hole.

It’s too early in the project to know for sure how often stars experience massive fails, but Scott Adams, a former Ohio State student who recently earned his Ph.D. doing this work, was able to make a preliminary estimate.

“N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we’ve been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae,” he said.

"This is just the fraction that would explain the very problem that motivated us to start the survey.”

This illustration shows the final stages in the life of a supermassive star that fails to explode as a supernova but instead implodes under gravity to form a black hole. From left to right: the massive star has evolved to a red supergiant, the envelope of the star is ejected and expands, producing a cold, red transient source surrounding the newly formed black hole. Some residual material may fall onto the black hole, as illustrated by the stream and the disk, potentially powering some optical and infrared emissions years after the collapse.

Credits: NASA, ESA, and P. Jeffries (STScI)

To study co-author Krzystof Stanek, the really interesting part of the discovery is the implications it holds for the origins of very massive black holes—the kind that the LIGO experiment detected via gravitational waves. (LIGO is the Laser Interferometer Gravitational-Wave Observatory.)

It doesn’t necessarily make sense, said Stanek, professor of astronomy at Ohio State, that a massive star could undergo a supernova—a process which entails blowing off much of its outer layers—and still have enough mass left over to form a massive black hole on the scale of those that LIGO detected.

“I suspect it’s much easier to make a very massive black hole if there is no supernova,” he concluded.

Adams is now an astrophysicist at Caltech. Other co-authors were Ohio State doctoral student Jill Gerke and University of Oklahoma astronomer Xinyu Dai. Their research was supported by the National Science Foundation.

More information: S. M. Adams et al. The search for failed supernovae with the Large Binocular Telescope: confirmation of a disappearing star, Monthly Notices of the Royal Astronomical Society (2017). doi.org/10.1093/mnras/stx816.  On rxiv: https://arxiv.org/abs/1609.01283

The Ohio State University release is here.  The STScI news release (with additional pictures) is here.

Contacts:

- Christopher Kochanek, 614-292-5954; Kochanek.1@osu.edu

- Krzysztof Stanek, 614-292-3433; Stanek.32@osu.edu

- Scott Adams, 626-395-8676; smadams@caltech.edu

Written by Pam Frost Gorder, 614-292-9475; Gorder.1@osu.edu

A Trojan in retreat

For at least a million years, an asteroid orbiting the “wrong” way around the sun has been playing a cosmic game of chicken with giant Jupiter and about 6,000 other asteroids sharing the giant planet’s space, says a report published in the latest issue of Nature.

The asteroid is the only one in the solar system known to have an opposite, or retrograde, orbit around the sun while at the same time sharing a planet's orbital space, says researcher and co-author Paul Wiegert of University of Western Ontario’s Department of Physics and Astronomy.

Jupiter shares its orbit with more than 6,000 Trojan asteroids (white), which travel in the same direction as the planet. But one of the planet’s companions is an outlier, traveling in the opposite direction. Planets and asteroids  have been enlarged to make them visible. 

All but fewer than 100 of the million or so known asteroids in our solar system travel around the sun in the same direction as Earth and the other planets (prograde motion). But asteroid 2015 BZ509 (“BZ” for short) circles the other way around – moving against the flow of all other asteroids in the giant planet’s orbital entourage (retrograde motion).

Put another way, it’s as if Jupiter were a monster truck on a track circling the sun, and the asteroids in Jupiter’s orbit are sub-compact cars all whizzing along in the same direction. BZ is the rogue — driving around the track in the wrong direction — and it does so every single lap, and has done so for thousands of laps for a million years or more.

So how does it avoid colliding with Jupiter? Jupiter’s gravity actually deflects the asteroid’s path at each pass so as to allow both to continue safely on their way, Wiegert says. Co-author Martin Connors of Athabasca University, adds: “Passes relatively near Jupiter take place twice on each body's orbit around the sun, but one is inside Jupiter's orbit, the other outside, so the disturbing effects of Jupiter, remarkably, cancel out.“

Little is known about the asteroid, which was discovered in January, 2015. It has a diameter of about three kilometers and may have originated from the same place as Halley's comet, which also has a retrograde orbit. The team hasn’t been able to determine yet if BZ is an icy comet or a rocky asteroid.

Images of 2015 BZ509 obtained at the Large Binocular Telescope Observatory (LBTO) that established its retrograde co-orbital nature. The LBTO has two 8.4 meter-wide main mirrors side-by-side, hence the two images taken in different color filters. The bright stars and the asteroid (circled in yellow) appear black and the sky white in this negative image. What are those weird white dots, spots and stripes? They are imaging artifacts in these raw images.

But their analysis – based on complex calculations and on observations through the Large Binocular Camera on the Large Binocular Telescope (LBT) on Mt. Graham, Arizona, during a span of 300 days — show BZ is somehow able to maintain a stable orbit even as an outlier. For co-author Christian Veillet of the LBT Observatory, this is a new step in a 15-year-long collaboration among the three co-authors, which until now, has been devoted to prograde asteroids sharing Earth’s orbit.

The calculations conducted by the team show the orbit has been stable for at least a million years and will be stable for at least a million more. Learning more about the asteroid provides another intriguing glimpse into previously unknown and unmapped features of our solar system, says Wiegert, adding that “the detective work has just begun.”

More information and video clips are available here. The Letter in Nature can be found here.

DDO 68: Among Galaxies, a Flea, but a Voracious One

Even a dwarf galaxy with very low mass is capable of accreting smaller nearby galaxies, according to an international team of astronomers led by Francesca Annibali of INAF, the Italian National Institute for Astrophysics. This result has been achieved thanks to observations of the region surrounding the dwarf galaxy DDO 68, which has a total stellar mass of only 100 million solar masses, roughly one thousandth of our Milky Way. 

In the new study, Annibali and collaborators took advantage of  the sensitivity and the large field of view of the LBT. The team discovered that DDO 68, a dwarf galaxy located in an isolated region of space defined as a "void," is actually surrounded by a number of smaller satellite galaxies, and is accreting them. 

Follow this link to know more about this discovery!