InSight mission

Land­ing site

The landing site for the InSight mission in Elysium Planitia
The land­ing site for the In­Sight mis­sion in Ely­si­um Plani­tia
Image 1/3, Credit: NASA/JPL/USGS (MOLA).

The landing site for the InSight mission in Elysium Planitia

For the In­Sight mis­sion, a land­ing area was sought that had to meet sev­er­al sci­en­tif­ic cri­te­ria, but above all space sys­tems en­gi­neer­ing cri­te­ria. For a se­cure en­er­gy sup­ply from so­lar pow­er and to avoid ex­treme di­ur­nal and sea­son­al tem­per­a­ture vari­a­tions, it could not be too far north or south of the equa­tor, it had to be flat and, as far as pos­si­ble, not cov­ered by rocks. Af­ter a long se­lec­tion pro­cess, en­gi­neers and sci­en­tists se­lect­ed an area in a plain south­west of the large vol­canic com­plex sur­round­ing Ely­si­um Mons. The cho­sen site is in Ely­si­um Plani­tia, north of the Mar­tian equa­tor and the high­land bor­der – just a few hun­dred kilo­me­tres north of Gale Crater (be­low the ‘4’ in the lat­i­tude la­bel), in which the NASA rover Cu­rios­i­ty has been driv­ing since 2012. The im­age is a sec­tion of a glob­al to­po­graph­ic map of Mars; blue and green are low-ly­ing ar­eas, yel­low and red are el­e­vat­ed ter­rain. The im­age is about 5000 kilo­me­tres wide.
Waves of seismic rays (P and PKP waves) on Mars
Waves of seis­mic rays (P and PKP waves) on Mars
Image 2/3, Credit: DLR

Waves of seismic rays (P and PKP waves) on Mars

Mod­el of waves of seis­mic rays (P and PKP waves) on Mars.
Flight over the In­Sight land­ing site in Ely­si­um Plani­tia
Video 3/3, Credit: DLR (CC-BY 3.0).

Flight over the InSight landing site in Elysium Planitia

Credit: DLR (CC-BY 3.0).
Length: 01:20
On 26 Novem­ber 2018, the NASA In­Sight probe land­ed on Ely­si­um Plani­tia on Mars at 4.5 de­grees north and 135.9 de­grees east. This video shows an over­flight over the land­ing site and its sur­round­ings. The video was based on a dig­i­tal ter­rain mod­el gen­er­at­ed with stereo im­age da­ta ac­quired by DLR's High Res­o­lu­tion Stereo Cam­era (HRSC) of the DLR.

The InSight probe landed on Mars on 26 November 2018. The landing site only has a few geological features. It was chosen because it represented minimal risk to the instruments boring down towards Mars' interior. As small inaccuracies in flight control and atmospheric effects during the descent may lead to deviations from the planned course, a sufficiently large area had to be selected – typically an elongated ellipse in the direction of flight. The InSight landing ellipse is 140 kilometres long and 30 kilometres across. In addition, it was important for the small penetrometer (or 'mole') of the HP3 heat flow probe to be able to penetrate the soil as easily as possible. This means that the site could not be rocky.

Based on data from earlier orbiter missions (primarily camera data and thermal inertia measurements – the speed with which the surface material reacts to temperature changes – captured from orbit), the landing site was predicted to have sand with low cohesion and thermal conductivity, resembling quartz sand on Earth, and a very low incidence of rocks (a few per cent) that might block the mole’s path deep down. It may be assumed that the frequency of the rocks will decrease with depth, as per the famous muesli or Brazil nut effect – if a bag of muesli containing pieces of different sizes is gently shaken for a period of time, upon opening it the smallest pieces will be found at the bottom of the bag, and the largest ones on top – like Brazil nuts. At a depth of three to 17 metres, however, there may be a layer of hard volcanic basalt rock.

A range of criteria is normally used when building seismological measuring stations on Earth. These include logistical considerations such as the accessibility of the site or the presence of a fixed power supply, but are primarily based on geological information such as known geological structures, the surface material and the position of epicentres in the past. As seismology works on the basis of a similar concept to medical ultrasound scanning, seismic waves traverse the area of interest – usually epicentres – and seismometers are normally located on different sides of the area in question.

However, researchers can only guess at how marsquakes are distributed across the planet. There is no infrastructure on the surface, and maintenance during regular visits is not possible. As such, the most important criterion for the site was the greatest possible security for the landing itself.

For some seismological techniques, the position of the seismometer is actually of secondary importance. A large meteorite impact could, for instance, cause the whole planet to vibrate at its resonant frequency and cause its overtones to vibrate like a bell, so this natural frequency provides important information about large-scale structures.

That said, the landing site offers various interesting options. One of the key objectives of the InSight mission is to measure the radius of Mars' core. The landing site is within sight of the Tharsis Massif, thought to be the most seismically active place on the planet. Part of it lies within the 'core shadow', beyond the distance at which the core shadows wave propagation by deflecting them towards the centre of the planet like a magnifying glass. These and other effects, as well as the time taken by waves to arrive at the seismometer, will allow the core to be measured. Tharsis is also at a suitable distance to measure waves that come from almost vertically below and thus study the crust immediately beneath the seismometer with precision. This process was developed on Earth in the 1980s and 1990s and has since become a standard method for measuring the thickness of the crust.

  • Elke Heinemann
    Ger­man Aerospace Cen­ter (DLR)
    Ger­man Space Agen­cy at DLR
    Strat­e­gy and Com­mu­ni­ca­tions
    Telephone: +49 2203 601-2867
    Königswinterer Straße 522-524
    53227 Bonn
  • Prof.Dr. Tilman Spohn
    HP³ Prin­ci­pal In­ves­ti­ga­tor
    Ger­man Aerospace Cen­ter (DLR)

    DLR In­sti­tute of Plan­e­tary Re­search
    Telephone: +49 30 67055-300
    Fax: +49 30 67055-303
    Linder Höhe
    51147 Köln
  • Ulrich Köhler
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Rutherfordstraße 2
    12489 Berlin
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