Private lunar lander challenges ideas about lunar volcanism

Blue Ghost’s first measurements test long-held man-on-the-moon explanation

A long spacecraft shadow falls across the moon’s surface beneath a black sky.

The first measurements from a private spacecraft on the Moon could reopen an old debate about why the Earth-facing side of the Moon looks the way it does.

Instruments aboard Firefly Aerospace’s Blue Ghost lander have discovered that underground heat at its landing site may not differ as much as scientists hoped from heat measured at the Apollo landing sites, the researchers reported in several talks March 17 at the Lunar and Planetary Science Conference in Woodlands, Texas. The result could reshape thinking about how the moon’s familiar dark spots form.

Almost all of the Moon’s lava flows are concentrated on its near side, in dark plains that give us the man on the moon. Scientists have long argued that a concentration of heat-producing chemical elements on the visible side contributed to the existence of widespread volcanism there. So, on March 2, 2025, Blue Ghost landed outside the heat-rich terrain in an impact basin called Mare Crisiumto see if it was really cooler there.

“The idea was that if we went out of this region, we could eliminate any internal bias and get a direct measurement from the outside,” says planetary geophysicist Robert Grimm of the Southwest Research Institute in Boulder, Colorado, who presented some of the results. “We hope Mare Crisium is far enough away [from the heat-rich terrain] that it represents the normal moon, the background moon.

Several Apollo missions from the 1960s and 1970s landed in ancient lunar lava flows called Maria. THE rocks brought back by astronauts were rich in elements that scientists collectively call KREEP, because of the elements they contain. The researchers assumed that the composition was similar in rocks across the Moon.

So it was a surprise in the late 1990s when NASA’s Lunar Prospector spacecraft discovered radioactive proxies for these elements concentrated in a region that includes many nearby lava flows — but almost nowhere else. This region is now called Procellarum KREEP Terrane, or PKT.

All these radioactive elements could have provided enough heat melt the mantle beneath the PKT, creating volcanic flows there but not on the rest of the moon, scientists proposed in 2000. But without measurements from outside the PKT, they couldn’t be sure.

This is where Blue Ghost comes in.

Radioactive elements such as heat-producing thorium are surprisingly clustered in part of the Moon’s near side, as this false-color map shows. Blue Ghost landed in a (circled) basin outside this region to see if the moon’s temperature was different in another location. On this map, white marks the highest thorium concentrations, purple the lowest.NASA

The lander carried two instruments capable of probing the moon’s internal temperature, one that drilled nearly a meter below the lander to measure heat flow, and another that inferred temperatures up to about 200 kilometers away.

If lava flows in the seas were primarily caused by heat-producing elements, the temperature under Mare Crisium should be different from that under the Apollo landers, Grimm says. After all, Blue Ghost landed in a place believed to be out the PKT.

But the temperatures were surprisingly close. The measurements of the Blue Ghost drill were comparable to those of similar instruments on Apollo 15 and 17geophysicist Seiichi Nagihara of Texas Tech University in Lubbock reported at the meeting. And measurements at greater depth differed from Apollo 12 by less than 230 degrees Celsiusrather than the expected 700 degrees.

To explain the results, Grimm cites measurements from another lunar orbiter called GRAIL, which in 2013 found that the lunar crust is thinner within the PKT than elsewhere on the Moon. Perhaps volcanism was easier there because there was simply less crust through which magma could fight to reach the surface, he says.

“I think [Blue Ghost’s finding] it reverses a quarter century of thinking about PKT,” says Grimm.

Not everyone is convinced. That 200-degree difference could still be consistent with more heat-producing elements near Apollo 12 than at Mare Crisium, says planetary scientist Mark Wieczorek of the Institut de Physique du Globe in Paris, co-author of the study proposing the idea in 2000. More recent research also suggests that the PKT may be smaller than previously thought, meaning Apollo 12 could have being right on the edge of the region rather than well inside it.

The debate could be settled with another private mission plannedplanned for 2027, which will carry similar heat measuring instruments to Schrödinger Crater on the far side of the Moon. This will be a better test, since the far side lacks both Marian and heat-producing elements.

“Geophysicists might debate how to interpret the results,” says Wieczorek, “but we all agree that we need more measurements.”