15. July 2019
Small fragments of carbon-rich asteroids are too fragile to survive entry into Earth’s atmosphere

MAS­COT con­firms what sci­en­tists have long sus­pect­ed

Temperature measurements on Ryugu's surface
Tem­per­a­ture mea­sure­ments on Ryugu's sur­face
Image 1/6, Credit: MASCOT/DLR/JAXA

Temperature measurements on Ryugu's surface

Close-up of a rock ex­am­ined by DLR's MARA ra­diome­ter di­rect­ly on the sur­face of Ryugu. The yel­low ar­row shows the di­rec­tion of il­lu­mi­na­tion, the dot­ted line sep­a­rates the ob­served rock from the back­ground. The red area shows the part of the rock where the sur­face tem­per­a­ture was mea­sured by the MARA ra­diome­ter, the dot­ted line shows a ledge in the rock. The scale in the cen­tre of the im­age shows the di­men­sions at this dis­tance from the cam­era. The im­age was ac­quired by the DLR MAS­CAM cam­era on board MAS­COT.
MASCOT radiometer MARA
MAS­COT ra­diome­ter MARA
Image 2/6, Credit: DLR (CC-BY 3.0)

MASCOT radiometer MARA

The MARA ra­diome­ter is used to mea­sure the sur­face tem­per­a­ture on Ryugu in high res­o­lu­tion as well as the tem­per­a­ture dif­fer­ences dur­ing a full day/night cy­cle on the as­ter­oid.
The surface of Ryugus from a few metres
The sur­face of Ryu­gus from a few me­tres
Image 3/6, Credit: MASCOT/DLR/JAXA

The surface of Ryugus from a few metres

The ap­prox­i­mate­ly 20 im­ages ac­quired with the MAS­CAM cam­era on the MAS­COT lan­der dur­ing the de­scent show an ex­treme­ly rugged sur­face cov­ered with nu­mer­ous an­gu­lar rocks. Ryugu, a four-and-a-half bil­lion year-old C-type as­ter­oid has shown the sci­en­tists some­thing they had not ex­pect­ed, even though more than a dozen as­ter­oids have been ex­plored up close by space probes. On this close-up, there are no ar­eas cov­ered with dust – the re­golith that re­sults from the frag­men­ta­tion of rocks due to ex­po­sure to mi­crom­e­te­orite im­pacts and high-en­er­gy cos­mic par­ti­cles over bil­lions of years. The im­age from the tur­bu­lent ro­tat­ing MAS­COT lan­der was tak­en at a height of about 10 to 20 me­tres.
Close-up of Asteroid Ryugu
Close-up of As­ter­oid Ryugu
Image 4/6, Credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST, Kobe University, Auburn University

Close-up of Asteroid Ryugu

Be­tween June 2018 and Oc­to­ber 2019, the ap­prox­i­mate­ly one-kilo­me­tre-di­am­e­ter as­ter­oid 162173 Ryugu was the tar­get of the Japanese Hayabusa2 space­craft, which was launched in 2014. The 'Pere­grine Fal­con' ex­am­ined Ryugu from dif­fer­ent dis­tances with sev­er­al cam­eras, spec­trom­e­ters and a laser al­time­ter. Small land­ing mod­ules al­so di­rect­ly ex­plored the sur­face. The Ger­man Aerospace Cen­ter (DLR) pro­vid­ed the MAS­COT land­ing mod­ule, which was equipped with four ex­per­i­ments from Ger­many and France. Ryugu is a Near Earth Ob­ject (NEO); the as­ter­oid's or­bit comes close to that of Earth, but there is no dan­ger of col­li­sion. The ob­ser­va­tions of Ryugu al­so serve to char­ac­terise such car­bon-rich C-type as­ter­oids, the most com­mon group of mi­nor bod­ies. Hayabusa2 is cur­rent­ly on its way back to Earth, car­ry­ing sam­ples from two sites on Ryugu in a sealed cap­sule, which are due to be re­cov­ered in Aus­tralia in late 2020.
Asteroid lander MASCOT
As­ter­oid lan­der MAS­COT
Image 5/6, Credit: DLR (CC-BY 3.0)

Asteroid lander MASCOT

A to­tal of four in­stru­ments are in­stalled with­in the 30 x 30 x 20-cen­time­tre lan­der. A DLR ra­diome­ter and cam­era, to­geth­er with a spec­trom­e­ter from the In­sti­tut d'As­tro­physique Spa­tiale and a mag­ne­tome­ter from the TU Braun­schweig, are set to ex­am­ine the min­er­alog­i­cal and ge­o­log­i­cal com­po­si­tion of the as­ter­oid’s sur­face and gauge its sur­face tem­per­a­ture as well as the as­ter­oid’s mag­net­ic field. A built-in swing arm gives MAS­COT the re­quired propul­sion to make jump­ing ma­noeu­vres over the sur­face.
Asteroid lander MASCOT on board the Hayabusa2 space probe
As­ter­oid lan­der MAS­COT on board the Hayabusa2 space probe
Image 6/6, Credit: DLR (CC-BY 3.0)

Asteroid lander MASCOT on board the Hayabusa2 space probe

The Japanese Hayabusa2 space probe has com­plet­ed a 3200-mil­lion-kilo­me­tre long jour­ney car­ry­ing the Ger­man-French lan­der MAS­COT (Mo­bile As­ter­oid Sur­face Scout).

Ryugu and other asteroids of the common ‘C-class’ consist of more porous material than was previously thought. Small fragments of their material are therefore too fragile to survive entry into the atmosphere in the event of a collision with Earth. This has revealed the long-suspected cause of the deficit of this meteorite type in finds on Earth. Researchers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) have come to this conclusion in a scientific paper published in the journal Nature Astronomy. The results are based on high-resolution measurements of the surface temperature with the DLR radiometer MARA on board the German-French Mobile Asteroid Surface Scout (MASCOT) lander. On 3 October 2018, as part of the Japanese Hayabusa2 mission, MASCOT descended onto the almost one-kilometre-diameter asteroid Ryugu and sent spectacular images and physical measurements from the surface back to Earth.

“Ryugu surprised us,” says Matthias Grott, Principal Investigator for the MARA radiometer experiment at the DLR Institute of Planetary Research in Berlin and lead author of the study. “On the asteroid, we observed only larger fragments that are highly porous and probably very fragile.” Earlier telescopic infrared light curves of such carbon-rich asteroids acquired from Earth had been interpreted by researchers studying their thermal properties as bodies covered in sand- to pebble-sized particles. In total, 21 DLR scientists from institutes in Berlin, Bremen and Cologne participated in the study, together with international partners. “MASCOT has brought together DLR’s broad range of expertise in space research – from design, development and testing to experience in the scientific exploration of the Solar System,” says Hansjörg Dittus, DLR Executive Board Member for Space Research and Technology. “The first published results are impressive proof of this.”

Deficit in meteorite finds reveals the protection provided by Earth's atmosphere

Until now, only a few chondritic meteorites found on Earth have been identified as fragments of C-type asteroids, which are very common in the Solar System ('C' is the chemical symbol for the element carbon). Chondrules are small, millimetre-sized rock globules that formed in the solar nebula 4.5 billion years ago and are considered to be the basic building blocks of planet formation. "We can now confirm that fragments of these asteroids are very likely to break up further when they enter Earth’s atmosphere, and then usually burn up completely. This means that only the largest fragments reach the Earth’s surface,” explains Grott. “That is why meteorites from this type of asteroid are so rarely found on Earth.”

The good news is that, because of this, Earth’s atmosphere offers increased protection from C-type asteroids, which account for 75 percent of all asteroids. Ryugu is a C-class asteroid, a carbon-rich representative of the oldest bodies in the 4.5 billion-year-old Solar System, and thus a building block of planet formation. It is one of the oldest of the 17,000 asteroids with orbits known to intersect that of Earth. However, further research is necessary to determine the maximum asteroid size for which this atmospheric protection is effective.

The international research team led by Matthias Grott determined the increase and decrease of the surface temperature over the course of the asteroid’s roughly seven-and-a-half-hour diurnal cycle. This was accomplished by measuring the infrared radiation emitted by the surface during the day and at night, using the MARA radiometer. The MARA measurements made it possible to infer the thermal properties and density of the material. The data from MASCOT were transmitted to the Japanese Hayabusa2 spacecraft. The craft was located at an observing position three kilometres above the asteroid’s surface. From there, MASCOT sent all measurement and operational data to Earth.

MASCOT landed on asteroid Ryugu on 3 October 2018 by free falling at walking pace. Six minutes after separating from Hayabusa2 at an altitude of 42 metres, the lander touched down on the asteroid’s surface having followed a ballistic trajectory. MASCOT bounced back up several metres, before the 10-kilogram experiment package finally came to rest. A rotating swing arm allowed MASCOT to turn to the 'correct' side and ‘hop’ across the surface. In total, MASCOT was active on Ryugu for 17 hours, one hour longer than anticipated.

The gravitational attraction of Ryugu is 66,500 times weaker than that of Earth, so the small amount of momentum produced by the arm was sufficient. This technical innovation for an unconventional form of mobility on an asteroid surface was used for the first time in the history of space exploration as part of the Hayabusa2 mission. The Hayabusa2 mission on Ryugu will continue until the end of 2019, with the goal of returning samples of the asteroid material to Earth by 2020. On 11 July, Hayabusa2 successfully completed the second touchdown operation on the asteroid.

About the Hayabusa2 mission and MASCOT

Hayabusa2 is a Japanese space agency (Japan Aerospace Exploration Agency; JAXA) mission to the near-Earth asteroid Ryugu. The German-French lander MASCOT carried on board Hayabusa2 was developed by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) and built in close cooperation with the French space agency CNES (Centre National d’Etudes Spatiales). The scientific experiments on board MASCOT were devised by DLR, the Institut d’Astrophysique Spatiale and the Technical University of Braunschweig. The MASCOT lander and its experiments are operated and controlled by DLR with support from CNES and in constant interaction with the Hayabusa2 team.

The DLR Institute of Space Systems in Bremen was responsible for developing and testing the lander together with CNES. The DLR Institute of Composite Structures and Adaptive Systems in Braunschweig was responsible for the stable structure of the lander. The DLR Robotics and Mechatronics Center in Oberpfaffenhofen developed the swing arm that allowed MASCOT to hop on the asteroid. The DLR Institute of Planetary Research in Berlin contributed the MASCAM camera and the MARA radiometer. The asteroid lander was monitored and operated from the MASCOT Control Center in the Microgravity User Support Center (MUSC) at the DLR site in Cologne.

  • Falk Dambowsky
    Ger­man Aerospace Cen­ter (DLR)
    Me­dia Re­la­tions
    Telephone: +49 2203 601-3959
    Fax: +49 2203 601-3249
    Linder Höhe
    51147 Cologne
  • Matthias Grott
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search, Plan­e­tary Geodesy
    Telephone: +49 30 67055-419

  • Prof.Dr. Ralf Jaumann
    Freie Uni­ver­sität Berlin
    In­sti­tute of Ge­o­log­i­cal Sci­ences
    Plan­e­tary Sci­ences and Re­mote Sens­ing
    Telephone: +49-172-2355864
    Malteserstr. 74-100
    12249 Berlin
  • Tra-Mi Ho
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Space Sys­tems
    Telephone: +49 421 24420-1171
    Robert-Hooke-Straße 7
    28359 Bremen
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Livestream - Press conference about the MASCOT landing
Three hops in three asteroid days – MASCOT successfully completes the exploration of the surface of asteroid Ryugu
Credit: DLR (CC-BY 3.0)

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