An asteroid’s threatened impact may still impact planetary defenseby Jeff Foust
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| “Everything that we’ve been preparing started happening,” Fast, NASA’s acting planetary defense officer, said of 2024 YR4. |
However, for 2024 YR4, an object estimated to be between 40 and 90 meters across at the time, the impact probability did not immediately fall, but instead rose, soon going above 1%. That attracted more attention, and even some alarm, as more observations caused the probability to creep higher, reaching 3.1% by February 18. Online, some wondered if the risk was now high enough to prompt action of some kind.
A few days later, though, this particular threat vanished. Additional observations updated the asteroid’s orbit enough that there was effectively no chance of a collision in December 2032 or for the foreseeable future.
It was, though, an exercise of existing capabilities and procedures by NASA and others to respond to a potential impact threat. “Everything that we’ve been preparing started happening,” said Kelly Fast, NASA’s acting planetary defense officer, at a meeting of a National Academies committee at the end of March.
She noted that once the asteroid’s impact risk increased above 1%, it triggered a formal notification policy to both other government agencies as well as the International Asteroid Warning Network, a group of astronomers who could follow up on the discovery with additional observations. Also notified was the Space Mission Planning Advisory Group (SMPAG, or “same page”), where representatives of national space agencies discuss how to respond to any asteroid impact threats. It was the first time that formal notification process was used, she added.
“We’re going through the lessons learned right now to see what all worked well and what we learned from this we could utilize in future situations,” she said.
At a hearing last week of the House Science Committee’s space subcommittee, Nicky Fox, NASA’s associate administrator for science, offered a similar message. “We let the world see the science of planetary defense in action,” she said of the monitoring of 2024 YR4.
The formal notification “wrung out some of the kinks” in the process, she noted. That process included a meeting chaired by NASA’s acting administrator, Janet Petro, with officials from other agencies, who Fox noted had to be explained just what was going on because, in the first weeks of the new administration, were new to their jobs.
| “We have not seen the details of the budget yet,” Mainzer said of potential effects on NEO Surveyor. “From my perspective, we do not know the impact yet.” |
The case of 2024 YR4 brought a new spotlight to NASA’s planetary defense program, a tiny part of the agency—less than 1% of its 2024 budget—but one with outsized interest. In his opening remarks at last week’s hearing, Rep. Mike Haridopolos (R-FL), chairman of the space subcommittee, cited a July 2023 poll by the Pew Research Center where 60% of respondents said planetary defense should be a top priority for NASA, more than any other mission mentioned. (Sending humans to the Moon, by contrast, was a top priority for only 12% of respondents, with human missions to Mars a percentage point lower.)
NASA used the hearing to tout the progress of its next planetary defense mission, NEO Surveyor. The mission will send a small infrared space telescope to the Earth-Sun L-1 Lagrange point, 1.5 million kilometers from Earth. The goal of the $1.2 billion mission is to significantly increase the rate of NEO discoveries, helping NASA comply with a goal mandated by Congress two decades ago to find at least 90% of all such objects at least 140 meters across.
NEO Surveyor is scheduled to launch no later than June 2028, but is currently on track to launch as soon as the fall of 2027. “They are on schedule. They are within the budget that we confirmed for them” in 2022, Fox said at the hearing.
The only recent hiccup for the mission was a pause in work on the spacecraft’s telescope at JPL in January when the center was closed because of wildfires nearby. Fox said that team lost nearly a month of schedule due to that. “That does put the telescope on the critical path, but something has to be on the critical path,” she said. “The last child out of the house dictates what time you get to school.”
The biggest concern, it seemed at the hearing, was how astronomers would handle all of the data NEO Surveyor would return. Matthew Payne, director of the Minor Planet Center at the Smithsonian Astrophysical Observatory, said at the hearing that NEO Surveyor, along with the Vera Rubin Observatory in Chile, will soon provide the center with ten times the data on NEO than all other current sources combined.
“We’ve made, and must continue to make, improvements in our hardware and software and processes to ensure that the planetary defense community is able to utilize this wealth of new data to safeguard us all,” he said. That includes developing artificial intelligence capabilities to better identify NEOs in the data it receives.
| “A very reasonable question is whether NASA should, in fact, be spending more money on asteroid monitoring and defense, given the catastrophic risk to our country and civilization,” said Whitesides. |
However, the hearing took place amid the specter of budget cuts proposed for NASA’s science programs in the 2026 top-level, or “skinny,” budget request by the White House. Many Democratic members of the committee criticized the proposed cuts at the hearing, as well as similar steep reductions at other federal agencies, from NSF to FEMA, also involved in various aspects of planetary defense.
“It’s clear that planetary defense leverages many of our S&T [science and technology] agencies,” said Rep. Zoe Lofgren (D-CA), ranking member of the full committee. “Whether that expertise continues, I think, is now in question.”
How that will affect planetary defense, including NEO Surveyor, is unclear. “We have not seen the details of the budget yet,” said Amy Mainzer, a professor at UCLA who leads NEO Surveyor. “From my perspective, we do not know the impact yet.”
Fox noted that the budget released in early May singled out by name only two science missions, Mars Sample Return and Landsat Next. “We’ve had no direction to take any action based on the ’26 skinny budget,” she said. “NEO Surveyor is well-funded.”
Being on budget and on schedule for launch in two and a half years would seem to insulate NEO Surveyor from cuts. Yet the Nancy Grace Roman Space Telescope, also on budget and set to launch as soon as the fall of 2026, is reportedly targeted for cancellation in the budget.
 Scientists have called for repurposing the twin Janus smallsats, currently in storage, for an Apophis flyby mission. (credit: Lockheed Martin) |
One thing that NEO Surveyor, and planetary defense in general, may have going for it is support by the agency’s likely next administrator. “Personally, I think there is a lot of taxpayer-funded science that should be reviewed & potentially reduced, but planetary defense against NEO threats seems disproportionately underfunded relative to the likelihood and magnitude of the associated risks & consequences,” wrote Jared Isaacman on social media on February 14, near the peak of interest in 2024 YR4.
He didn’t elaborate on how much more money planetary defense should receive—or what other science should be reduced—but the idea of spending more on planetary defense does have advocates in Congress. “A very reasonable question is whether NASA should, in fact, be spending more money on asteroid monitoring and defense, given the catastrophic risk to our country and civilization,” said Rep. George Whitesides (D-CA) at the hearing. “That might be a conversation we can have in the coming months.”
There are concepts for missions that could be carried out if there is additional funding. The planetary science decadal survey, for example, recommended NASA pursue a “rapid response” mission to send a spacecraft to a small NEO, testing the ability to quickly carry out such a reconnaissance mission if there was a real impact threat.
There are also ongoing efforts to secure support for missions to study the near Earth asteroid Apophis both before and after it makes an April 2029 flyby of Earth, coming closer to the planet than satellite in geostationary orbit (although with zero risk of an impact.)
NASA has already repurposed the main spacecraft from the OSIRIS-REx asteroid sample return mission, now called OSIRIS-APEX, which will arrive at Apophis a couple months after the asteroid’s Earth flyby. There is interest, through, in missions going to Apophis before the flyby, enabling before-and-after characterization of any changes to the asteroid caused by tidal forces from the close flyby.
ESA has provided initial funding for one such mission, RAMSES, with full funding pending a decision at the agency’s next ministerial conference in November. The Japanese space agency JAXA is developing DESTINY+, a mission that will go to another NEO, Phaethon, but could fly by Apophis on its way to Phaethon.
Scientists continue to advocate for a NASA-led mission to Apophis before the flyby. One leading option is to use the twin Janus smallsats originally built for flybys of binary asteroids. Those spacecraft were put into storage when NASA canceled the mission in 2023 because delays in its rideshare launch on the Psyche mission kept it from carrying out that original mission.
Last fall, NASA issued a request for information (RFI) seeking concepts on how the Janus spacecraft could be repurposed for an asteroid mission. Responses to the RFI were due last fall but NASA has not provided an update since then.
In a document outlining the conclusions of an Apophis science workshop in April, scientists again advocated for NASA to act on potential reuse of Janus for Apophis. Noting that a workshop a year earlier called Janus the “highest recommendation” for a NASA-led pre-encounter mission, “we follow-up by urging NASA to issue a timely response to the Apophis 2029 Innovation Using the Janus Spacecraft Request for Information.”
| “If we can’t all unite on a large chunk of rock hurtling towards the planet,” Fox said, “what are we going to unite on?” |
The Janus RFI did not come up at the House hearing last week, where Fox noted a NASA effort to look at alternative concepts for a mission came up empty. “We looked at the possibility of partnering with non-traditional partners to be able to do that,” she said. “We didn’t find a viable path forward without significant budget from us that we actually didn’t have.”
She appeared to suggest that OSIRIS-APEX could handle the pre-encounter observations, as it can start observing Apophis a couple weeks before the Earth flyby. “Even though they’re going to be low-resolution, we’re going to have some really nice images of how the light and the brightness changes,” she said.
After the hearing, though, she said that NASA hasn’t ruled out using the Janus spacecraft for an Apophis mission. “We’re still discussing it,” adding it would depend on budgets for fiscal year 2026 and beyond.
There’s not much time to waste, with less than four years before Apophis makes it Earth flyby. “We collectively entreat and emphasize to our respective agencies, member states, funding sources, and all interested parties that time is of the essence for moving forward decisively in funding current science investigations proposed and underway,” the document stated, emphasizing the phrase “time is of the essence” in bold, italics, underlining, and yellow highlighting.
While 2024 YR4 doesn’t pose and impact threat to the Earth, it may yet impact planetary defense, if NASA and Congress see it as an opportunity to support the agency’s work on the topic even within constrained budgets.
“If we can’t all unite on a large chunk of rock hurtling towards the planet,” Fox said at the hearing, “what are we going to unite on?”
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