The Short and Long of It

Lori Glaze, Planetary Science Division DirectorWith less than three months until the September 26 Double Asteroid Redirection Test (DART) kinetic impact event, we are rapidly hurtling toward the mission’s culmination. DART — humanity’s first-ever demonstration of a planetary defense technique — is an anomaly in the Planetary Science Division’s (PSD’s) portfolio because the spacecraft is demolished at the moment its science really begins!

DART is on a direct and designed collision course with the Didymos binary asteroid system, which is the ideal target for this real-world demonstration of the kinetic impactor approach — impacting an asteroid to adjust its speed and path. Didymos (about 780 meters or 0.5 miles in diameter) poses no threat to Earth, and the fact that it is actually the larger member of a binary system makes it a perfect natural laboratory for this test. DART will aim for the smaller “moonlet” Dimorphos (about 160 meters or 525 feet in diameter) and will alter its orbit around Didymos.

When DART hits Dimorphos in a nearly head-on collision at a speed of about 22,531 kilometers per hour (14,000 miles per hour), the momentum of the spacecraft, plus the recoil from the ejecta blasted out of the impact crater, will be transferred to Dimorphos, resulting in a shortening of its orbital period. Right now, from Earth we can see (from the regular dimming of the telescopically measured light curve) that Dimorphos completes an orbit of Didymos every 11 hours and 55 minutes. We predict that the impact will cause Dimorphos’ orbit to shorten by several minutes, which will mean that it will orbit slightly closer to Didymos. This binary asteroid system, and the timing of impact, were chosen so that the collision occurs when the asteroids are passing close to Earth. This means that we will be able to obtain the highest-quality telescopic observations of the system in the weeks after the impact to see precisely how much Dimorphos’ orbital period has actually changed.

Although DART is accompanied by LICIACube [contributed by the Agenzia Spaziale Italiana (ASI)], which will capture images of the impact event and its effects on the surface of Dimorphos, the DART spacecraft itself carries only one scientific payload — the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO). DRACO is a high-resolution imager that will support navigation and targeting as DART approaches Dimorphos. The images it acquires before the impact will be streamed back to Earth in real time. I can’t wait to see Dimorphos grow larger and larger in the pictures and see the real character of this tiny asteroid in the final moments before DART meets its purposed fate.

From launch to impact, DART’s flight operations will last only 10 months — just a blink of an eye in comparison with some of our other planetary missions. It feels strange to be bidding farewell to DART almost as soon as we got to see it fly, but in recompense, I’m glad that we have recently decided to extend several of our ongoing missions after the conclusion of the 2022 Planetary Mission Senior Review (PMSR22) process.

Senior Reviews typically take place every three years and are the chance for us to examine our ongoing missions and the case for each to extend their science operations. This time around, eight missions were reviewed, including five Mars missions (MAVEN, Mars Science Laboratory, InSight, Mars Reconnaissance Orbiter, and Odyssey), as well as Lunar Reconnaissance Orbiter (LRO), OSIRIS-REx, and New Horizons. All missions submitted three-year extended mission proposals (except OSIRIS-REx, which proposed a nine-year extension to include an encounter with Apophis in 2029). These proposals were then reviewed (each independently) by a set of review panels, and we based our decisions upon their final reports.

The results of the PMSR22 are now available online, and I’m delighted to report that we elected to extend all eight missions. All of them will be extended for a further three years, with a few exceptions.

As already mentioned, OSIRIS-REx will be extended for nine years and will actually morph into a new mission with a new name — OSIRIS-APEX (APophis EXplorer). Once OSIRIS-REx, led by Principal Investigator Dante Lauretta (University of Arizona), has completed its return journey to Earth to drop off its sample capsule and precious cargo from Bennu, the spacecraft will head out on its journey toward Apophis, where it will give us a close-up look at this rubble-pile asteroid. Daniella DellaGiustina (University of Arizona) will be the new PI for OSIRIS-APEX.

New Horizons has been extended for two years, during which time it will make distant observations of Uranus and Neptune, with geometries not possible from Earth. The spacecraft’s cameras will also be used to map the very faint “cosmic background” at visible and ultraviolet wavelengths. In addition, New Horizons will explore the heliosphere outward of 54 AU. Its instruments will be used to study the motion of charged particles as they interact with the solar wind and to examine the large-scale structure of the heliosphere. Indeed, New Horizons will be given the opportunity to propose to become part of NASA’s Heliophysics System Observatory (HSO) at the end of this upcoming extended mission.

The shortest of all the extensions is for InSight, as we anticipate the spacecraft’s expected retirement. We have extended InSight until the end of this calendar year, or until the spacecraft ceases to operate because of reduced power. Although InSight continues to monitor seismic activity on Mars, buildup of dust on its solar panels means that the amount of power available for spacecraft operations is rapidly falling, and we expect science activities to cease later this summer or fall.

I don’t have space to describe the plans for all the other extended missions, but I encourage you to read the posted final report to find out more. And I want to give a special shout-out to our two particularly long-lived workhorses Odyssey (21 years old) and LRO (13 years old)!

As we prepare to say goodbye to some of our beloved missions in the coming months, let’s also be thankful for the prospect of many more years of fantastic science from so many of our amazing PSD missions. I’m also incredibly grateful to the PMSR22 team (led by Henry Throop and Lindsay Hays in PSD) and all the reviewers for their hard work and dedication, and especially to our mission teams, who sustain our missions and drive them forward in the pursuit of science and exploration.

— Lori S. Glaze, Director, NASA’s Planetary Science Division, July 2022