Finding Asteroids Before They Find Us
NASA’s Planetary Defense Program
Kelly Fast
Acting Planetary Defense Officer
NASA Planetary Defense Coordination Office
About the Lecture
NASA’s planetary defense program addresses one of the few natural hazards that can, in principle, be predicted years in advance and prevented: the impact of a dangerous near-Earth asteroid or comet. At the center of that effort is NASA’s Planetary Defense Coordination Office, established in 2016 to manage the agency’s work to find, track, characterize, and, when necessary, help develop options to mitigate hazardous near-Earth objects. Through its Near-Earth Object Observations Program, the office helps turn astronomical observations into practical risk assessment and response planning.
This lecture will describe how planetary defense has become an international enterprise as well as a national one. NASA’s coordination role extends beyond U.S. agencies to the International Asteroid Warning Network, which shares observations and threat information worldwide, and the Space Mission Planning Advisory Group, which brings together space agencies to examine possible reconnaissance and deflection responses. Both entities are endorsed by the United Nations. In that sense, planetary defense is not only a scientific and engineering challenge, but also a problem in global communication, informed decision-making, and preparedness.
The talk will also examine how these systems perform when a real object draws attention. The recent case of asteroid 2024 YR4 briefly raised concern because early calculations showed a small chance of Earth impact, before additional observations ruled out any significant Earth risk. NASA has described this episode as an example of how the planetary defense community refines risk as additional data arrive. It illustrated the importance of rapid orbit determination, transparent public communication, and it established channels for notifying governments and international bodies when a credible threat must be assessed.
Finally, the lecture will show that planetary defense is no longer limited to watching the sky. It now includes tested methods for changing an asteroid’s motion. NASA’s Double Asteroid Redirection Test was the first mission to demonstrate asteroid deflection by kinetic impact, and NASA’s planned NEO Surveyor mission is the first space telescope specifically designed to discover and characterize asteroids and comets that may pose a hazard to Earth. Together, these efforts contribute toward a strategy with two essential goals: discover hazardous objects as early as possible, and ensure that humanity has credible response options before an impact threat is discovered.
NASA Planetary Defense Coordination Office: https://science.nasa.gov/planetary-defense/
NASA Center for Near-Earth Object Studies: https://cneos.jpl.nasa.gov/
NASA page on asteroid 2024 YR4: https://science.nasa.gov/solar-system/asteroids/2024-yr4/
NASA DART mission: https://science.nasa.gov/mission/dart/
NASA NEO Surveyor mission: https://science.nasa.gov/mission/neo-surveyor/
International Asteroid Warning Network: https://iawn.net/
Space Mission Planning Advisory Group: https://www.cosmos.esa.int/web/smpag
United Nations Office for Outer Space Affairs, near-Earth objects: https://www.unoosa.org/oosa/en/ourwork/topics/neos/index.html
About the Speaker
Kelly E. Fast is Acting Planetary Defense Officer in NASA’s Planetary Defense Coordination Office at NASA Headquarters, where she also oversees the Near-Earth Object Observations Program, and NASA’s role in the International Asteroid Warning Network. Previously, she managed NASA’s Near-Earth Object Observations Program, as well as leading several research programs in NASA’s Planetary Science Division, and serving as Program Scientist for the MAVEN mission to Mars. Kelly has also been a visiting astronomer at NASA’s Infrared Telescope Facility on Maunakea and contributed to management activities involving both the IRTF and NASA’s participation in the Keck Observatory.
Kelly’s research has centered on planetary atmospheres, planetary defense, and the observational study of small bodies in the solar system. She worked with very high spectral resolution infrared instrumentation, including HIPWAC, to investigate ozone and atmospheric chemistry on Mars, atmospheric dynamics on Titan, and the atmospheric consequences of impact events on Jupiter.
Among notable aspects of her work, Kelly helped lead NASA’s programs for finding, tracking, and characterizing near-Earth objects, coordinated US and international planetary defense activity through NASA and the International Asteroid Warning Network, and played key programmatic roles connected to a variety of NASA missions and observing campaigns. She also contributed to important work on Martian ozone, Titan’s winds and composition, and Jupiter’s stratospheric response to impact events.
Among other honors and awards Kelly received NASA Headquarters Honor Awards for exceptional performance in management, operations, and the success of the Planetary Defense Coordination Office in detecting and warning of natural impact hazards to Earth. She has also been honored by the naming of main-belt asteroid 115434 Kellyfast in recognition of her contributions to planetary science.
Kelly earned a BS degree in Astrophysics at the University of California, Los Angeles, and an MS and PhD in Astronomy at the University of Maryland, College Park.
Minutes
On April 10, 2026, Members of the Society and guests joined the speaker for a reception and dinner at 5:45 PM in the Members’ Dining Room at the Cosmos Club. Thereafter they joined other attendees in the Powell Auditorium for the lecture proceedings. In the Powell Auditorium of the Cosmos Club in Washington, D.C., President Larry Millstein called the lecture portion of the 2,534th meeting of the Society to order at 8:12 p.m. ET (after the Artemis splashdown, as the safe recovery of “Integrity” and its crew was watched in real time in the Powell Auditorium). He began by welcoming attendees, thanking sponsors for their support, announcing new members, and inviting guests to join the society. Scott Mathews then read the minutes of the previous meeting which included the lecture by Bill Diamond, titled “Is There Life Out There?”. The minutes were approved as read.
President Millstein then introduced the speaker for the evening, Kelly Fast, of NASA’s Planetary Defense Coordination Office. Her lecture was titled “Finding Asteroids Before They Find Us”.
The speaker began by showing videos of the Chelyabinsk meteor, a superbolide that entered the Earth’s atmosphere over Russia in February 2013. She said that despite the fact that this object disintegrated before hitting the ground, it nonetheless caused damage and injury. She said that this minor event demonstrated why we would like to avoid impacts from larger, denser objects.
The speaker showed an animation of known near-Earth asteroids as of 1999, as compared to similar animations from 2009 and 2018. She described how the search for near-Earth objects was formalized in 2016 with the formation of the Planetary Defense Coordination Office, and the codification of systems and protocols for issuing “Potentially Hazardous Object” notifications, both in the US and internationally.
Fast showed an image representing the various tasks associated with Planetary Defense, including: Search, Detect & Track, Characterize, Plan & Coordinate, Mitigate, and Assess. She gave details concerning each of these tasks, describing some of the infrastructure and strategies employed by NASA to achieve these goals. With respect to mitigation, she said “This is a natural disaster that we could potentially do something about.” The speaker described the “National Strategy and Action Plan” for near-Earth object hazards. She indicated that the critical goals of this plan are to: enhance detection, develop reconnaissance and disruption technologies, and to increase international cooperation.
The speaker listed several NASA-funded asteroid survey programs, including: ATLAS, CSS, Pan-STARRS, and LINEAR. Fast showed images of several telescopes being used in these surveys. The locations of these telescopes included: the Continental United States, Hawaii, South Africa, Chile, Spain, and Australia. She said that NASA funds many other telescopes around the world to follow-up on initial observations, in order to accurately predict their trajectories.
Fast presented information on the numbers of near-Earth asteroids discovered to date: more than 41,000 total, with about 11,000 greater than 140 meters, and more than 870 greater than 1 kilometer in diameter. She showed data indicating an exponential growth in the number of near-Earth asteroids discovered in recent years. The speaker said that NASA’s goal was to find at least 90% of the near-Earth objects that are 140 meters in diameter or larger. She claimed that current estimates indicate that they have identified about 46%. Fast said that the International Astronomical Union was responsible for identifying, designating, and computing initial orbit estimates. Subsequently, the Center for Near-Earth Object Studies at JPL was responsible for high precision orbit computations.
The speaker discussed a number of asteroid impacts that were predicted by the Planetary Defense Coordination Office. “2024 RW1”, an asteroid about 1 meter in diameter, was discovered in 2024. Detailed observations allowed such accurate estimates of the impact site and the time of impact, that several people were able to capture the event with cell phone cameras. She described how international collaboration led researchers to believe that asteroid “2024 YR4” had a 1.8% chance of striking the Earth in 2032. She said that additional observations narrowed the uncertainty, leading to the conclusion that 2024 YR4 had a “near zero” probability of impacting the Earth within the next 100 years.
The speaker described the details of how the Planetary Defense Coordination Office notifies other agencies within the US government (the President, FEMA, and State Department), and subsequently notifies the United Nations, the European Space Agency, and the International Asteroid Warning Network.
Fast then described the DART mission, launched in 2021, which delivered a kinetic impactor to the asteroid Dimorphos, a small asteroid orbiting the larger Didymos, in September of 2022. She indicated that this successful mission demonstrated the ability to deflect the trajectory of asteroids. She showed video acquired from the DART mission, saying “there is something kind of strange when you have a bunch of scientists and engineers cheering over the destruction of a very expensive spacecraft.”
The speaker ended her talk by showing a short, promotional, NASA video called “Planetary Defenders”, which emphasized the fact that we have the ability to alter and control future impact events.
The lecture was followed by a Question and Answer session.
A member asked whether the mission of the Planetary Defense Coordination Office included comets and space weather, two phenomenon which could potentially threaten the entire planet. Fast responded that comet impacts, although much less likely than asteroid impacts, are monitored by her office, but that space weather was monitored by other offices and agencies.
A member asked if there had been any experimental testing on the use of lasers to alter the trajectory of asteroids. Fast responded that the most basic technique for altering trajectory is kinetic impact, but that several other strategies have been considered. These included ion beams, gravity tractors, nuclear detonations, and lasers. She said the primary problem with lasers is getting the required power levels on board a spacecraft, and that some of the other technologies are more mature.
A member asked, given the current “fleet of telescopes”, how much lead time would we likely have for an object larger than 140 meters in diameter? Fast responded that a 60-meter object was discovered in 2024 that was predicted to come close to the Earth in 2032, so with a larger object, there is a chance that we would have many years of advanced notice, however, “It is tough to say”.
After the question and answer period, President Millstein thanked the speaker and presented her with a PSW rosette, a signed copy of the announcement of her talk, and a signed copy of Volume 17 of the PSW Bulletin. He then announced speakers of up-coming lectures and made a number of housekeeping announcements. He adjourned the 2,534th meeting of the society at 9:47 pm ET.
Temperature in Washington, DC: 16.1° Celsius
Weather: Partly Cloudy
Dinner attendance: 42
Lecture attendance:
In person: 81
Live Stream: 34
For a total of 115 viewers
Views of the video in the first two weeks: 307
Respectfully submitted, Scott Mathews: Recording Secretary