OSIRIS-REx captures 'super-resolution' view of Bennu

This "super-resolution" view of asteroid Bennu was created using eight images obtained by NASA's OSIRIS-REx spacecraft on Oct. 29, 2018, from a distance of about 205 miles (330 km). The spacecraft was moving as it captured the images with the PolyCam camera, and Bennu rotated 1.2 degrees during the nearly one minute that elapsed between the first and the last snapshot. The team used a super-resolution algorithm to combine the eight images and produce a higher resolution view of the asteroid. Bennu occupies about 100 pixels and is oriented with its north pole at the top of the image. OSIRIS-REx executes third asteroid approach maneuver. NASA's OSIRIS-REx spacecraft has executed its third Asteroid Approach Maneuver (AAM-3). The trajectory correction maneuver (TCM) thrusters fired in a series of two braking maneuvers designed to slow the spacecraft's speed relative to Bennu from approximately 11.7 mph (5.2 m/sec) to .24 mph (.11 m/sec). Due to constraints that science instruments not be pointed too closely to the Sun, this maneuver was designed as two separate burns of approximately 5.8 mph (2.6 m/sec) each, to accomplish a net change in velocity of around 11.5 mph (5.13 m/sec). The mission team will continue to examine telemetry and tracking data over the next week to verify the new trajectory.

The maneuver targeted the spacecraft to fly through a corridor designed for the collection of high-resolution images that will be used to build a shape model of Bennu.

The OSIRIS-REx spacecraft is in the midst of a six-week series of final approach maneuvers. AAM-1 and AAM-2, which executed on Oct. 1 and Oct. 15 respectively, slowed the spacecraft by a total of approximately 1,088 mph (486 m/sec).

The last of the burns, AAM-4, is scheduled for Nov. 12 and will adjust the spacecraft's trajectory to arrive at a position 12 miles (20 km) from Bennu on Dec. 3.

OSIRIS-REx executes third asteroid approach maneuver

NASA's OSIRIS-REx spacecraft has executed its third Asteroid Approach Maneuver (AAM-3). The trajectory correction maneuver (TCM) thrusters fired in a series of two braking maneuvers designed to slow the spacecraft's speed relative to Bennu from approximately 11.7 mph (5.2 m/sec) to .24 mph (.11 m/sec). Due to constraints that science instruments not be pointed too closely to the Sun, this maneuver was designed as two separate burns of approximately 5.8 mph (2.6 m/sec) each, to accomplish a net change in velocity of around 11.5 mph (5.13 m/sec). The mission team will continue to examine telemetry and tracking data over the next week to verify the new trajectory. The maneuver targeted the spacecraft to fly through a corridor designed for the collection of high-resolution images that will be used to build a shape model of Bennu. The OSIRIS-REx spacecraft is in the midst of a six-week series of final approach maneuvers. AAM-1 and AAM-2, which executed on Oct. 1 and Oct. 15 respectively, slowed the spacecraft by a total of approximately 1,088 mph (486 m/sec). The last of the burns, AAM-4, is scheduled for Nov. 12 and will adjust the spacecraft's trajectory to arrive at a position 12 miles (20 km) from Bennu on Dec. 3.

The formation of large meteorite craters is unraveled

About 66 million years ago, a meteorite hit the Earth of the Yucatan Peninsula in what is now Mexico. This event triggered a mass extinction that eradicated approximately 75 percent of all species and ended the era of dinosaurs. Like Prof. Dr. Ulrich Riller of the Institute of Geology of the University of Hamburg and co-workers report in "Nature", the hitherto mysterious formation of the crater and its mountaneous peak ring. The peak rises in the middle of the crater above the otherwise flat crater floor. In the future, these findings can help to decipher the formation of the largest craters in our solar system. Much has been written and discussed about the gigantic crater with a diameter of about 200 kilometers, the center of which lies near the Mexican port city of Chicxulub. How the giant crater took its form has been a mystery until today. In particular, the formation of a circular series of hills could not be explained in detail. This so-called peak ring rises in the crater several hundreds of meters above the shallow ground and can therefore be found in other large craters in our solar system. The structural geologist Prof. Dr. Ulrich Riller and an international team of scientists have now succeeded in describing for the first time the extreme mechanical behavior of rocks in the event of a large meteorite impact.

The researchers found the evidence in the Chicxulub Crater as part of Expedition 364 of the International Ocean Discovery Program (IODP) and the International Continental Scientific Drilling Program (ICDP).

Computer simulations have shown that craters this size form within a few minutes. This means that solid rock behaves like a fluid for a short time and solidifies very quickly during cratering.

As the science team reports in the current issue of the journal "Nature", their research supports the hypothesis of so-called acoustic fluidization, where rock behaves like a viscous mass through contemporary pressure changes (vibrations).

The obtained drill cores display a variety of zones of broken rock, which the team considers to be evidence of transient fluidity of the rock. The team was able to transmit the results in numeric models, which simulate the exact formation of the crater and peak ring.

"The results of our research team have far-reaching consequences for understanding the formation of large impact craters in our solar system," explains Prof. Riller.

Hayabusa-2 team prepares for asteroid sample collection

JAXA's (Japan Aerospace Exploration Agency's) Hayabusa-2 mission is on track to return samples from its target asteroid, 162173 Ryugu, a C-type near-Earth asteroid (NEA). The past month has seen the successful deployment of two rovers and a lander. The mission focus is now on the successful retrieval and return of a surface sample. Two members of the Planetary Science Institute's (PSI's) science staff are on the Hayabusa-2 science team as part of NASA's Participating Scientist program, a cooperative effort between NASA and JAXA. Deborah Domingue is a member of both the Optical Navigation Camera (ONC) and Near Infrared Spectrometer (NIRS3) instrument teams. Lucille Le Corre is a Co-Investigator on the ONC team. Their focus, over the past several months, has been in support of data processing and analysis of Hayabusa-2 data for landing site selection. The Hayabusa-2 engineering team's safety constraints restrict where the spacecraft can safely touch down. These constrains include regions of 100 meters diameter with an average slope less than 30 degrees, boulder heights less than 50 centimeters, and an absolute temperature less than 370 degrees Kelvin (97 degrees Celsius). This limited the selection to a region plus or minus 30 degrees from the equator. The challenge of the science team was to find a region of scientific interest that met the engineering constraints.

The biggest hurdle seems to be finding regolith in a place that is comprised of boulders less then 50 centimeters, within a 100-meter-diameter region. The lack of a powdered, fine-grain regolith on asteroid Ryugu will make it difficult for the Hayabusa-2 spacecraft to collect a sample to be returned to Earth.

"Unlike other asteroids we have visited, Ryugu has no powder, no fine-grain regolith. That makes selecting a place to sample more challenging," said PSI's Domingue. "We are helping characterize the surface to optimize landing site selection."

"Since the approach phase began last June, my main goal was to support the Hayabusa2 team in the preparation of touchdown operations," said Le Corre.

"In order to assess the sampleability of Ryugu's terrains I have worked on generating products such as ONC image mosaics and local topographic models. Our data show that the Hayabusa-2 team has to carefully select a sampling site to avoid the numerous boulders present on the surface."

Domingue has been working on regolith analysis, with a focus on the photometric and spectral characterization of the surface. Le Corre has been focused on mapping the surface, combining both the geologic features with the topographic properties. The goal of the science team is to select a site that will return a sample of the least processed material, yet meet the engineering constraints.

"We need to have a very detailed understanding of the nature of the surface to be sampled in order to maximize the realization of the science goals of the mission," Domingue said.

Domingue and Le Corre participated in a press conference during the 50th annual meeting of the American Astronomical Society's Division for Planetary Sciences (DPS) in Knoxville, Tenn.

The DPS press conference brought the community up to date on the activities of the mission and the preparation for sample retrieval.

The press conference panel consisted of several Hayabusa-2 team members, including Masaki Fujimoto, the head of ISAS/JAXA, Hikaru Yabuta, the lead of the landing site selection committee and the multi-scale regolith characterization team, Ralf Jaumann, the lead for the European Space Agency's (ESA's) MASCOT lander, and Eri Tatsumi, the ONC team instrument scientist.