Asteroid Defense, Lunar Risks and Gravity Mysteries: What NASA Is Working On

The National Aeronautics and Space Administration (NASA) came into global focus in early April. After more than 50 years, it once again sent a human crew toward the Moon. In addition, the Artemis 2 crew, including the first woman, the first Black astronaut on a lunar mission, a Canadian and the American commander, observed the far side of the Moon with their own eyes for the first time.

However, perhaps the most famous US agency, apart from the White House or the Federal Bureau of Investigation (FBI), is working on many other projects of comparable importance. NASA routinely monitors extreme weather, wildfires, fluctuating ocean levels and even asteroids circling Earth. That work came to the fore four years ago, when one space rock was deliberately deflected.

Deflecting an Asteroid

In September 2022, the Double Asteroid Redirection Test (DART) spacecraft slammed into the asteroid Dimorphos, causing its orbit to shift. It was not an accident. The DART mission explored whether the trajectory of a body that could potentially hit Earth can be deflected.

Dimorphos is thought to be a satellite orbiting the asteroid 65803 Didymos. While the asteroid has a diameter of about 780 m, its moon is only about 160 m across. The force with which the spacecraft struck the smaller of the pair reportedly surprised astronomers.

In addition to changing its orbit around the larger asteroid, Dimorphos slightly altered the motion of the system. The orbital period sped up, according to a report in The New York Times.

"If we ever discover an Earth-bound asteroid, we need to change its orbit around the Sun," research leader Rahil Makadia of the University of Illinois warned. The goal, according to the report, was to "prove that if a deadly space rock threatened Earth in the future, humans could deflect it".

The moon’s roughly 12-hour orbital period around the larger asteroid was shortened by 33 minutes. Astronomers also found that the system’s 770-day orbit around the Sun was shortened by about 150 milliseconds.

Although the shift appears small, it represents a breakthrough in at least two ways. Even a small time change can have a noticeable effect over distances of millions of kilometers. It is also the first time a human-made object has altered the motion of a celestial body.

Motivated by this success, the space agency launched the Near-Earth Object Surveyor mission, which could detect dark, risky asteroids that remain nearly invisible from terrestrial observatories, as CNN noted. That could become relevant for planetary defense as early as 2032, when Canadian astronomers expect to see debris from the Moon hitting Earth.

Moon Impact

A key role in this scenario is played by asteroid 2024 YR4, discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Chile in December 2024.

The asteroid, roughly the size of a 15-story building, poses only a minimal risk to Earth. The probability of impact is estimated at about 1%. However, according to researchers led by astronomer Paul Wiegert at Western University in Canada, there is a higher probability that it could hit the Moon.

The study predicts a potential impact on 22 December 2032. Such an event "would release energy comparable to 6.5 megatons of TNT and create a crater approximately one kilometer in diameter", the study noted.

"We estimate that such an impact could release up to 100 million kg of lunar material that would exceed the escape velocity of the Moon," Wiegert’s team warned, adding that only in a small fraction of scenarios would ejecta be directed toward Earth.

While debris from the Moon may not reach Earth’s surface, particles between 0.1 and 10 mm in diameter could damage satellites in orbit. This threat could persist for years or even decades, according to the researchers, opening a debate about extending planetary defense to lunar orbit.

However, new research by the European Space Agency (ESA) Planetary Defence Office called these calculations into question, concluding that 2024 YR4 will pass the Moon at a distance of about 20,000 km. NASA later ruled out any likelihood of a lunar impact.

The Hole Under Antarctica

But NASA is not just watching what happens in space. The Jet Propulsion Laboratory (JPL) at the California Institute of Technology (Caltech) is one of the space agency’s most important institutions. In addition to developing probes such as Galileo and Pathfinder, it also manages the GRACE experimental program, which monitors changes in the Earth’s gravitational field.

Although the Earth appears to be round, mountains and oceans create elevations that cannot easily be described using basic geometric shapes. The different rocks that make up the planet also have different densities, causing observable differences in the gravitational field. For these variations, the Gravity and Climate Observation (GRACE) program uses the term “geoid”.

According to the GRACE model, gravitational force is higher in the Andes, Turkey, Greenland and Indonesia, while it is lower in the Indian Ocean and Hudson Bay in Canada. A particular “geoid minimum”, meaning an area with lower gravitational force, is Antarctica, which has also recently attracted interest.

The gravitational force beneath Antarctica has slowly begun to decrease, as scientists Alessandro Forte of the University of Florida and Petar Glisovic of the Paris-based Institute for Terrestrial Physics have noted. The pair successfully modelled the movement back to the time of the anomaly’s formation 70 million years ago.

The geophysicists created the first detailed map of the gravity minimum using an unusual tool, earthquakes. “Seismic waves from earthquakes travel through the planet and change speed and direction when they hit materials with different compositions and densities,” Science Alert explained.

“Imagine doing a CT scan of the entire Earth, but we do not have X-rays like in a doctor’s office,” Forte explained. “We have earthquakes. Seismic waves provide the ‘light’ that illuminates the interior of the planet,” he added.

Based on the available information about seismic activity, the scientists created a three-dimensional model of the density of the Earth’s mantle [the layer beneath the Earth’s crust, ed.], which they compared with GRACE’s model. The models were almost exactly the same.

In addition to depicting the evolution of changes in the gravitational field, the model also described shifts in the Earth’s rotational axis. Fifty million years ago, the gravity field beneath Antarctica dropped rapidly as the surrounding tectonic plates began to melt and sink below the surface. This corresponded with a shift in the Earth’s axis.

It may also explain the glaciation of the southernmost continent. Forte and Glisovic admitted that this remains speculative, but the decrease in gravitational force appears to be related to sea-level shifts.

According to the hypothesis, the decline of the geoid could have caused a drop in sea level at the continent’s shores, potentially affecting the growth of the ice sheet, estimated to have begun 34 million years ago.

It was NASA’s work that was used to test this geological model. Along with planetary defense and monitoring climate change, astronomers have more than enough to do.

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