Apophis T–7 Years:
Knowledge Opportunities for the Science of Planetary Defense

Apophis T–7 Years Workshop logo

The Apophis T-7 Years Workshop was held virtually May 11–12, 2022. Participation at the workshop, which was organized by the Lunar and Planetary Institute, was broadly international, with 150 registrants representing more than 20 countries delivering 40 presentations. Particularly noteworthy was the participation and valuable contributions of students and new postdocs exploring the topic for the first time. Online participants spanned 18 time zones. The workshop theme centered on the knowledge opportunities for the science of planetary defense that might be gained through observations of the asteroid 99942 Apophis, which will make a close flyby of Earth on April 13, 2029. (Coincidentally, that will be Friday the 13th…) At the flyby distance of 5.8 Earth radii, Apophis will reach a distance that is nearer than geosynchronous satellites, yet outside the classic Roche limit. Yet even outside the Roche limit, gravitational torques by Earth on Apophis are likely to alter its spin state and may induce seismic effects on Apophis sufficient to mobilize its regolith.

The workshop provided the opportunity for the international planetary science community to come together and share current data for the known physical and orbital characteristics of Apophis, as well as current best models for measurable effects on Apophis that may be induced by Earth. As an overview, it was noted that an object as large as Apophis (340 meters, or 1115 feet) makes such a close approach to Earth about once every 1000 years. Measurements of this “natural experiment” therefore provide an extremely rare opportunity to deduce the internal structure properties of a potentially hazardous asteroid (PHA).

Workshop presentations and findings noted and endorsed the concurrent activity of a NASA Specific Action Team (SAT) that is preparing a report quantifying the best estimates for measurable effects, including prioritization and methods (groundbased and in situ) to achieve them. Also noted were the specific findings and recommendations of the 2022 Planetary Decadal Survey report supporting the detailed study of Apophis during its encounter. The approved extended mission for OSIRIS-REx, to be renamed OSIRIS-APEX (Apophis Explorer) was described, bringing outstanding capabilities to study Apophis.

Orbital dynamics do not allow OSIRIS-APEX to arrive until after the date of Apophis’ Earth encounter. Workshop participants noted that pre-encounter measurements remain an open challenge to be solved. Four mission concepts were presented to address the pre-encounter measurement challenge. A workshop finding noted that time is of the essence for identifying a funding pathway for bringing these concepts to maturity and possible flight. Also identified was a need for international collaboration on an Apophis campaign, so that multi-wavelength experiments (radar, radio) and possible spacecraft operations at the time of close approach do not create mutual interference. An additional goal of an Apophis campaign would be to be at the forefront of public information on the Apophis 2029 flyby being a science opportunity and not a hazard. Apophis will miss Earth, but we will be watching to learn the most that we can.

For more information about the Apophis T-7 workshop , including links to the program and abstracts, visit the meeting website at https://www.hou.usra.edu/meetings/apophis2022/.

— Summary provided by Richard Binzel