DAN is a Russian instrument in the scientific payload of the Curiosity rover (Curiosity, Mars Science Laboratory project, NASA).

The DAN operating concept is based on the methods of nuclear physics. The instrument generates short (about 1 ms in duration), but powerful pulses of neutrons. Up to 10 million particles of 14 MeV energy are emitted per pulse. Emitted neutrons penetrate into the Martian subsurface and interact with the nuclei of the main rock-forming elements.

If one measures the energy and detection time of neutrons, having escaped from the soil after the pulse, one can estimate the content of various atoms in the subsurface, primarily hydrogen. The distribution of hydrogen in the subsurface is a key to understanding of how much hydrated minerals or water ice permafrost are there. DAN is sensitive enough to detect water content as low as 0.1%.

These data are essential, when one studies the processes of the Red Planet's hydrological evolution and searches for areas with conditions that could favour the existence of primitive life.

The predecessor of the DAN experiment is the HEND instrument, a part of Mars Odyssey orbiter (NASA, launched in 2001) payload, also made by the Space Gamma Spectroscopy Laboratory of IKI (now the Nuclear Planetology Department). It was thanks to HEND data that water ice was first discovered in the regolith beneath the Mars surface. However, HEND has been measuring neutrons formed naturally by cosmic rays in the subsurface, while DAN has been sounding the surface along the rover’s traverse with neutron pulses.

DAN began its work on the surface of Mars on August 7, 2012. In 10 years (until August 20122) American-Russian scientific team of the DAN experiment, part of rover control team, held >5000 operation sessions, providing day-to-day planning of science program as to what concerns the DAN experiment. About 1500 sessions of neutron sounding were made, which makes roughly 3 sessions in a week. The neutron generator of the instrument has emitted more than 5 million neutron pulses, which many times exceeds its nominal lifetime. It is still operating on the surface of Mars, having shown no failures.

The surface of Gale crater, according to DAN data, has variable salinity. Water content varies from 2 to 6 %. High water content is seen in the regions with hydrated minerals, which were formed in the early period of Martian history, when the crater was filled with water. Significant content of chlorine in the surface is established, up to 2.5% by weight. It is yet another argument in favour of the hypothesis that Gale crater was an ancient lake. These data shed new light on the processes, which reigned on Mars in different epochs of its evolution.

DAN Scientific Instruments

• DAN-DE detector and electronics unit — ³He industrial neutron proportional counters
• DAN-ING pulse neutron generator — developed at Dukhov Automatics Research Institute on the basis of industrial pulse generator

Main parameters

• Neutrons energies: from thermal to 14 MeV
• Temporal resolution: 1–3 ms
• Spatial resolution: ~1 m
• Vertical resolution (maximal penetration depth): ~1 m