How NASA is making autonomous rovers for the moon

Mini-moon rovers, how earth has seen its warmest summer yet, a solution for the “wild boar paradox”, and more in this edition of Science Notebook.

A pair of plastic prototypes of the CADRE rovers driving in formation during a test at the Jet Propulsion Laboratory last year. | Photo Credit: NASA/JPL-Caltech

NASA proposes to send a trio of miniature rovers to the moon to see how well they can cooperate with one another without direct radio input from the earth. A project named CADRE (Cooperative Autonomous Distributed Robotic Exploration) is developing robots that can operate autonomously, and thereby boost the efficiency of future missions. By taking simultaneous measurements from multiple locations, the rovers are meant to show how multi-robot missions can potentially enable new science or support astronauts.

Currently slated to be aboard a lander in 2024 as part of NASA’s Commercial Lunar Payload Services initiative, CADRE’s three small rovers will be lowered onto the Reiner Gamma region of the moon via tethers. Each of these four-wheeled rovers is about the size of a carry-on suitcase and will drive and locate a sunbathing spot where it will open its solar panels and charge up. The rovers will spend about 14 earth days—the daylight hours of a single lunar day—conducting experiments designed to test their capabilities.

“Our mission is to demonstrate that a network of mobile robots can cooperate to accomplish a task without human intervention, autonomously,” said Subha Comandur, the CADRE project manager. “It could change how we do exploration in the future. The question for future missions will become ‘How many rovers do we send, and what will they do together?’”

Warmest summer

THE earth just had its hottest three months on record. This is according to the World Meteorological Organization on the basis of a dataset released by the Copernicus Climate Change Service (C3S), which is implemented by the European Centre for Medium-Range Weather Forecasting (ECMWF). It was the hottest August on record, by a large margin, and the second hottest month ever after July 2023, according to the C3S. August as a whole is estimated to have been around 1.5°C warmer than the pre-industrial average for 1850-1900.

The year so far (January to August) is the second warmest on record behind 2016, when there was a powerful warming El Nino event. August as a whole saw the highest global monthly average sea surface temperatures on record across all months, at 20.98°C. Temperatures exceeded the previous record (March 2016) every single day in August.

Antarctic sea ice extent remained at a record low level for the time of year, with a monthly value 12 per cent below average, by far the largest negative anomaly for August since satellite observations began in the late 1970s.

Arctic sea ice extent was 10 per cent below average but well above the record minimum of August 2012.

Bavarian wild boar paradox finally solved

AFTER the Chernobyl nuclear accident in 1986, the consumption of mushrooms was discouraged because of high radioactive contamination, and the meat of wild animals was also severely affected for several years. The radioactive contamination of deer and roe deer decreased over time as expected but remained inexplicably high in the case of Bavarian wild boar meat, making it unsuitable for consumption to this day. This “wild boar paradox” was unsolved until now, when scientists at the Vienna University of Technology and the Leibniz University of Hannover provided an explanation. The work was recently published in Environmental Science and Technology.

 The radioactive contamination of deer and roe deer decreased over time but remained inexplicably high in the case of the Bavarian wild boar (in picture). | Photo Credit: USAG Bavaria/Environmental Division on Facebook

The most important element for the radioactivity of the samples is cesium-137 (Cs-137), with a half-life of about 30 years, which means that half of the material would have decayed by itself after 30 years. Radiation exposure to food usually declines much faster. Cesium that had dispersed since Chernobyl was washed out by rainwater or bound to minerals or perhaps migrated deep into the soil, so is no longer absorbed by plants and animals in the same quantities as immediately after the accident.

Different sources of radioactive isotopes have different physical fingerprints: fallout from the Chernobyl nuclear accident, for example, has an isotope fingerprint that is different from that of atmospheric nuclear weapons tests. They not only release Cs-137 but also Cs-135, an isotope with a much longer half-life, and the ratio of the two depends on the cesium’s origin.

Quantifying Cs-135 accurately, however, is difficult. Its long half-life means radiation detectors are not good enough, according to Georg Steinhauser, the scientist who led the investigation. “You have to work with mass spectrometric methods and go to relatively great lengths to distinguish it precisely from other atoms. We have now succeeded in doing that,” he said. The researchers analysed the meat of 48 boars in 11 Bavarian districts between 2019 and 2021.

The results showed that while a total of about 90 per cent of the Cs-137 in central Europe came from Chernobyl, a large proportion of the cesium in wild boar meat, up to 68 per cent in some samples, is attributable to nuclear weapons testing.

The boars like to dig up deer truffles (Elaphomyces) from the ground; radioactive cesium accumulates in these subterranean mushrooms. | Photo Credit: YouTube

The reason for this apparently lies in the boars’ very special food preferences: they particularly like to dig up deer truffles (Elaphomyces) from the ground, and the radioactive cesium accumulates in these subterranean mushrooms (20-40 cm below the ground) with a long-time delay. “The cesium migrates downwards through the soil very slowly, sometimes only about 1 mm per year,” said Steinhauser. Deer truffles are thus only now absorbing the Cs-137 that was released in Chernobyl as against the Cs-135 from “old” nuclear weapons tests, which would have got absorbed quite some time ago. Thus, the contamination of wild boar meat is not expected to decrease significantly in the next few years because some of the cesium from Chernobyl is only now being incorporated into the truffles.