Jupiter Moon Europa’s Ice Spikes May Endanger Robot Landers

Penitentes may reach up to 50 feet tall and occur about every 23 feet in Europa's equatorial regions.

New Horizons mission captured image of the icy moon Europa rising above Jupiter's cloud.
NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Penitentes may reach up to 50 feet tall and occur about every 23 feet in Europa's equatorial regions.

Jupiter’s ocean moon Europa is one of the worlds in the solar system that scientists think may possibly host life. Exploring the 1,900-mile-wide satellite, however, would pose extraordinary challenges.

Findings of a new study have suggested that the equatorial regions of Europa, which harbors an ocean of salty liquid water beneath its icy crust, may be studded with ice spikes.

The structures known as penitentes may reach up to 50 feet tall and occur about every 23 feet. Their presence could make navigating the moon difficult.

Study researcher Dan Hobley, from the School of Earth and Ocean Sciences at Cardiff University in Wales, and colleagues said that the findings have important implications on NASA’s plan to send a robot lander that will hunt for signs of life on Europa.

“Clearly, the paper suggests very strongly that the tropics of Europa are going to be spiky, and it would be unwise to plan to land there without a specially adapted lander,” Hobley said in a statement to Space. “It would probably be safer to land further away from the equator!”

On Earth, penitentes are sculpted through sublimation, a process wherein sunlight transforms snow or ice in a dry environment into water vapor without melting it.

Hubble captures image of planet Jupiter.
  NASA, ESA, and the Hubble SM4 ERO Team / Getty Images

Because parts of the ice sublimate faster than the others, surface depressions form. These spots concentrate sunlight and speed up sublimation even more, carving the icy spikes.

The structures have not yet been directly observed in Europa, but researchers used data from Jupiter missions to develop computer simulations that can show how penitentes form on the icy moon.

In their study published in the journal Nature Geoscience on Oct. 8, Hobley and colleagues found that the conditions on the moon could support the growth of penitente fields along the equator, where the surface receives strong sunlight. The researchers also found that temperatures in the area can dip to around –200° Celsius.

Hobley and colleagues said that the icy structures may explain the odd temperature readings and radar observations previously collected.

Mapping based on radar signals from the Arecibo Observatory, for instance, hinted uneven features on Europa’s features. NASA’s Galileo missions also showed abnormally cold temperature readings during nighttime flies, which could be data from an oblique angle that measured only the frozen tips of the penitentes instead of the whole surface.

“Puzzling properties of the radar and thermal observations of Europa’s equatorial belt can be explained by the presence of penitente fields in this region,” the researchers wrote in their study. “The implications of penitente fields at potential landing sites should motivate further detailed quantitative analysis.”