Discovery from the BBC World Service: Planetary Defence, Asteroids and Moonquakes

Overview

In this Discovery episode, the BBC World Service takes you to AGU sessions where geoscience and space science intersect. The focus is planetary defence, the near-Earth asteroid 2024 YR4, and what a potential Moon impact in 2032 could reveal about lunar structure and the broader space environment that affects our technology on Earth.

Key Threads

• Asteroid YR4: initial close approach expectations, refined observations, and the Moon’s greater but still uncertain risk
• Space weather and solar-terrestrial science, including the Punch mission and wide-field solar observations
• Moonquakes and Artemis-era seismology plans for the Moon’s far side

As the program moves from headlines to science, it highlights how space phenomena can influence satellites, GPS, and communications here on Earth, and what new missions may reveal about the architecture of our planetary neighborhood.

Overview

Discovery from the BBC World Service brings together experts and journalists at AGU, linking geoscience and space science to illuminate how Earth sits in a dynamic solar system. The episode centers on planetary defence, but also expands into solar weather, the Moon, and the evolving science that connects Earth and space.

Planetary Defence and the 2024 YR4 Asteroid

The session revisits the asteroid 2024 YR4, discovered in late December 2024, which briefly raised concern about a possible Earth impact in 2032. Early orbit estimates suggested a nonzero probability, but follow-up observations refined the trajectory and reduced Earth risk. JWST was called upon to measure the asteroid’s size and gather additional positions, strengthening the assessment. The Earth’s fate looked clear, but the Moon’s fate remained more nuanced.

"there was a 12, 3% chance that it might hit the Earth." - Andy Rivkin, planetary astronomer, Johns Hopkins University Applied Physics Laboratory

As data accumulated, the audience learned that although Earth appears safe, there is a non-negligible chance the Moon could be affected. The current estimate points to about a 4% chance of YR4 impacting the Moon in 2032, a scenario that would drive both scientific interest and public engagement. The plan includes upcoming JWST observations in February to further refine the asteroid’s trajectory and to determine how close the Moon’s path might come.

Experts stress that the longer the interval between initial and subsequent measurements, the more precise the orbit becomes, which in turn informs planetary-defence strategies and lunar science.

"we plan to have two different observing shots at it in February, a couple of days apart" - Andy Rivkin, planetary astronomer

Solar Weather and the Punch Mission

The episode then pivots to the solar-terrestrial connection, explaining how space weather can disrupt technology on Earth. Punch, the polarimeter to unify the corona and heliosphere, is designed to image eruptions along a wide field of view, enabling 3D tracking of solar storms as they traverse the solar system. This capability mirrors the leap in weather forecasting that happened when satellites allowed us to observe hurricanes in motion rather than from a few distant measurements.

"we can see them in 3 dimensions all the way across the solar system" - Craig DeForest, principal investigator for the Punch mission

The mission seeks to address two major questions: the transient solar storms that propagate through the heliosphere, and the ambient solar wind, including the alphane zone, which remains poorly measured. Parker Solar Probe and Punch together promise a comprehensive view of the space environment that governs how satellites and GPS respond to solar activity.

Moon Studies: Moonquakes and Lunar Seismology

Back on the Moon, researchers discussed moonquakes and the planned seismometer deployments on the far side as part of NASA’s Artemis program. The near side is covered by maria and familiar features, but the far side holds a markedly different structure, potentially revealing deeper interior properties and how the Moon records the giant impact that formed the Earth-Moon system around 4.5 billion years ago.

Seismology experts outlined a networked approach: land seismometers on the Moon and maintain continuous Earth-based observations to observe lunar seismic events, using timing and travel-time analyses to infer internal structure. The plan includes Artemis-3 and Artemis-4 missions, with seismometers on the far side, to build a three-dimensional picture of the Moon’s interior over time.

There is also discussion of lunar impact events, including how micrometeoroid impacts generate observable flashes on the Moon, which in turn trigger seismic waves that may be detected by lunar seismometers. A network of telescopes on Earth would monitor these flashes to correlate with seismic data from the Moon, enabling precise mapping of subsurface properties.

"the exosphere is huge, and it's because the constituents are atomic hydrogen" - Laura Waldrop, Carruthers mission

Outlook: Science Bonanza or Public Spectacle?

The program closes by contemplating the potential outcomes if YR4 were to impact the Moon in 2032. Such an event would be a science bonanza and a public spectacle, potentially delivering unprecedented data on lunar material, seismic propagation, and the Moon’s outer layers. The discussion also notes that even if the Moon is impacted, Earth would likely experience minimal direct harm, while satellite lifetimes could be affected by debris and dust dynamics. The episode ends with a forward-looking note: more data, refined models, and stronger collaborations between planetary science and space physics will deepen our understanding of how Earth fits within a space-faring solar system.

Next week, the Discovery team returns to terra firma to cover the Mississippi delta, Katrina’s lessons, and the future of ice and life’s origins, continuing AGU coverage from the Earth’s perspective.

"there would be a science bonanza as well as a public spectacle" - Patrick King, seismology researcher