Asteroid Bennu, KBO Ultima Thule Get New Year’s Visitors From Planet Earth

The asteroid Bennu and Kuiper Belt Object (KBO) Ultima Thule got New Year’s visitors from planet Earth as 2018 rolled into 2019 — robotic probes sent by NASA.  The asteroid sample return mission OSIRIS-REx entered orbit around Bennu for the first time at 2:43 pm December 31 Eastern Standard Time (EST) and New Horizons flew past Ultima Thule at 12:33 am January 1 EST.  Both are collecting data to help scientists understand how our solar system formed and evolved.

Bennu is 70 million miles away from Earth, which sounds like a long distance until compared with Ultima Thule, which is 4 billion miles away.  OSIRIS-REx is on a mission to return a sample of Bennu to Earth and will remain at Bennu until 2020 before heading home.  New Horizons, on the other hand, will keep going further and further into space for eternity, sending back data hopefully for the next two decades.

Launched in September 2016, OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) arrived at Bennu at December 3.  It spent the rest of the month conducting a preliminary survey to determine what orbital characteristics were necessary to complete its task.

Bennu is the smallest object ever orbited by a spacecraft, just 494 meters (1,614 feet) in diameter.

Staying in orbit is a challenge.  Dan Wibben of KinetX Aerospace, the mission’s maneuver and trajectory design lead, explains that solar radiation and thermal pressure from the asteroid’s surface can outweigh its “tenuous” gravitational force, which is 5-millionths as strong as Earth’s.  It is sticking close by, just 1 mile (1.75 kilometers) from its center, the closest any spacecraft has orbited a celestial object.

OSIRIS-REx will spend the next 18 months or so collecting more data about Bennu’s mass, gravity, and surface characteristics before briefly touching the surface to collect a sample with its Touch-and-Go Sample Acquisition Mechanism (TAGSAM) for return to Earth.  That sample is expected back in September 2023.

Dante Lauretta of the University of Arizona Lunar and Planetary Laboratory (UALPL) is the Principal Investigator (PI) for the mission and UALPL leads the science team and mission’s science observation planning and data processing.  The spacecraft was built by Lockheed Martin Space in Denver and it provides flight operations, communicating through NASA’s Deep Space Network (DSN) of antennas in the United States, Spain and Australia.  The project is managed by NASA’s Goddard Space Flight Center.

Spacecraft operations are considered essential and allowed to continue despite the partial government shutdown, which includes NASA, though participation of federal employees is limited.

That applies to New Horizons as well.  It was built by and is operated at the Johns Hopkins University Applied Physics Laboratory (JHUAPL) in Laurel, MD.  NASA’s DSN is the only way to communicate with that spacecraft, too.

New Horizons was launched in 2006 with the primary goal of flying past Pluto.  It did so successfully in 2015 and then continued on its way out of the solar system.  Pluto is in a portion of the solar system called the Kuiper Belt and is the first KBO visited by a spacecraft.  New Horizons PI Alan Stern of the Southwest Research Institute (SwRI) convinced NASA to continue the mission beyond Pluto aiming for another KBO.

Using the Hubble Space Telescope, in 2014 scientists discovered a very small KBO one billion miles (1.6 billion kilometers) past Pluto that was on New Horizon’s path. Officially designated 2014 MU69, it got the nickname Ultima Thule (“a place beyond the known horizons”) after a public naming contest.  It is just 20 miles (30 kilometers) long.

It is one of hundreds of thousands of KBOs, which are thought to be composed of ice, rock, or both.  Those in circular orbits like Ultima Thule have remained there at temperatures close to absolute zero since the solar system formed 4.5 billion years ago, frozen in time.

Little is known about KBOs other than Pluto.  New Horizons is a chance to study one up close. It passed Ultima Thule just 2,200 miles (3,500 kilometers) from the surface though it was travelling very fast  — 32,000 miles per hour (52,000 kilometers per hour) — and had only one chance to take one row of images.

It takes about 6 hours and 7 minutes for a radio signal to travel one-way between the spacecraft and Earth.  New Horizons made its closest approach to Ultima Thule at 12:33 am EST this morning and collected images and data.  At about 10:30 am, mission controllers received the anxiously awaited “phone home” signal telling that them the spacecraft is fine and its data recorders are full.  Because of the distance involved and the low power transmitter (just 15 watts of power) it will take 20 months for all the data to arrive.

The New Horizons team has not received data from the flyby yet, but at a press conference this morning they released an image they received just before the flyby.  Stern joked that people could laugh because it is so blurry, but until the higher resolution flyby images are received, it is the best available.

Some say the shape is reminiscent of a bowling pin.  Others say a peanut.

Media events will be held tomorrow and Thursday to share flyby images and other data, but as noted it will take almost two years to get all the data and images back.  Stern quipped that the entire New Horizons mission has been one of “delayed gratification” considering how long it took to get the mission approved and launched and then the nine year trip to Pluto and another three to Ultima Thule.

He hopes it is not over, though.  New Horizons will continue on its path in perpetuity.  Stern expects its radioisotope power source to remain functional through the end of the 2030s. For the next decade, it will remain in the Kuiper Belt and he will try to convince NASA to allow another KBO flyby in the future.

OSIRIS-REx and New Horizons are two of the three missions developed under NASA’s New Frontiers program of mid-sized PI-led missions.  New Horizons was the first; OSIRIS-REx the third.  The other is Juno, a spacecraft currently orbiting Jupiter.  Development is cost-capped at $850 million. NASA is currently selecting the fourth in the series. In December 2017 it narrowed the choices from 12 to two:

• CAESAR, led by Cornell University’s Steve Squyres, which would return a sample from the comet 67P/Churyumov-Gerasimenko that was visited in 2014 by the European Space Agency’s Rosetta spacecraft and its Philae lander, or
• Dragonfly, led by JHUAPL’s Elizabeth “Zibi” Turtle, which would send a drone-like rotorcraft to Saturn’s moon Titan that could fly from place to place to study its atmosphere and surface, which is thought to have rivers and lakes of methane and ethane.

The final decision is expected in July 2019.