Ekkehard Kührt

German Aerospace Center (DLR) | DLR · Department of Asteroids and Comets

Between 2014 December 31 and 2015 March 17, the OSIRIS cameras on Rosetta documented the growth of a 140m wide and 0.5m deep depression in the Hapi region on Comet 67P/Churyumov-Gerasimenko. This shallow pit is one of several that later formed elsewhere on the comet, all in smooth terrain that primarily is the result of airfall of coma particles. W...

Between 2014 December 31 and 2015 March 17, the OSIRIS cameras on Rosetta documented the growth of a 140 m wide and 0.5 m deep depression in the Hapi region on Comet 67P/Churyumov–Gerasimenko. This shallow pit is one of several that later formed elsewhere on the comet, all in smooth terrain that primarily is the result of airfall of coma particles....

The CoPhyLab (Cometary Physics Laboratory) project is designed to study the physics of comets through a series of earth-based experiments. For these experiments, a dust analogue was created with physical properties comparable to those of the non-volatile dust found on comets. This ‘CoPhyLab dust’ is planned to be mixed with water and CO2 ice and pl...

The Near-Earth Asteroid (162173) Ryugu has been investigated by the JAXA Hayabusa2 mission. Hayabusa2 successfully returned samples from two sites of Ryugu’s surface to Earth in December 2020. Part of this mission was the deployment of the MASCOT lander which studied Ryugu’s surface in detail. Ryugu is a rubble-pile asteroid covered in boulders and...

The near-Earth asteroid (162173) Ryugu, the target of Hayabusa2 space mission, was observed via both orbiter and the lander instruments. The infrared radiometer on the MASCOT lander (MARA) is the only instrument providing spectrally resolved mid-infrared (MIR) data, which is crucial for establishing a link between the asteroid material and meteorit...

Comets are remnants from the formation of the Solar System, and contain the most pristine material available today for deciphering the physical and chemical conditions of this process. As such, they are very interesting candidates for sample return missions, as indicated for example by the recent mission proposals CAESAR, CONDOR, and CORSAIR to the...

The JAXA MMX sample return mission to the martian moons will deliver a rover to the surface of Phobos that will investigate the landing area using its navigation cameras (NavCams), its regolith facing cameras (WheelCams), its Raman spectrometer (RAX), as well as its mid infrared radiometer (miniRAD). The distance that can be travelled by the Rover...

The Comet Physics Laboratory (CoPhyLab) is an international research program to study the physical properties of cometary analog materials under simulated space conditions. The project is dedicated to studying, with the help of multiple instruments and the different expertise and background from the different partners, the physics of comets, includ...

The CoPhyLab (Cometary Physics Laboratory) project is designed to study the physics of comets through a series of earth-based experiments. For these experiments, a dust analogue was created with physical properties comparable to those of the non-volatile dust found on comets. This "CoPhyLab dust" is planned to be mixed with water and CO$_2$ ice and...

Lunar surface temperature variations provide key information about the thermophysical properties of the regolith. To date, temperatures have been measured using telescopes and orbiter instruments, providing information from mid-to long infrared (IR) wavelengths. Here we report on temperature measurements in the short wavelength IR at centimeter sca...

Dynamically different groups of comets and active asteroids with orbits at 2–5 a. u. show dust activity in varying degrees and forms. A photometric study and comparison of physical parameters can help to classify the mechanisms and nature of the activity for such objects. We present new observations using broadband photometry of 15 active objects i...

Dynamically different groups of comets and active asteroids with orbits at 2 - 5 a. u. show dust activity in varying degrees and forms. Photometric study and comparison of physical parameters can help to classify mechanisms and nature of the activity for such objects. We present new observations using broadband photometry of 15 active objects in th...

Both observations of C-type near-Earth asteroids and laboratory investigations of carbonaceous chondritic meteorites provide strong evidence for a high microporosity of C-type asteroids. Boulder microporosity values derived from in-situ measurements at the surface of the rubble-pile NEA (162173) Ryugu are as high as 55 %, which is substantially hig...

The processes leading to the formation of planetary systems leave behind a significant mass of small bodies - up to 35 Earth masses depending on the model [1] - orbiting at large heliocentric distance, and observed around 20% of Sun-like stars [2]. It is established that those bodies play an important role in the migration of gas giants away from t...

Aims. The tensile strength of granular matter is of great importance to our understanding of the evolution of comets and to our attempts to reproduce processes on cometary surfaces in laboratory experiments. In this work, we investigate the tensile strength of three different materials and their mixtures, which can be used as cometary analog materi...

This chapter reviews the estimates of the dust-to-gas and refractory-to-ice mass ratios derived from Rosetta measurements in the lost materials and the nucleus of 67P/Churyumov-Gerasimenko, respectively. First, the measurements by Rosetta instruments are described, as well as relevant characteristics of 67P. The complex picture of the activity of 6...

Aims. We provide a measurement of the seasonal evolution of the dust deposit erosion and accretion in the Hapi region of comet 67P/Churyumov-Gerasimenko with a vertical accuracy of 0.2–0.9 m. Methods. We used OSIRIS Narrow Angle Camera images with a spatial scale of lower than 1.30 m px−1 and developed a tool to monitor the time evolution of 22 bou...

We will briefly recapitulate the beginning of modern cometary physic. Then we will assess the results of the cometary flyby missions previous to ESA’s Rosetta rendezvous with comet 67P/Churyumov–Gerasimenko. Emphasis is given to the physical properties of cometary nuclei. We will relate the results of the Rosetta mission to those of the flybys. A m...

Plain Language Summary Magnetic measurements in space near and on solar system bodies such as asteroids can provide important information about their formation history and their material properties. Hayabusa2, a Japanese mission, visited asteroid Ryugu, a type of asteroid (carbon rich) not visited before. Ryugu is a rubble pile, that is, an agglome...

Comet 49P/Arend-Rigaux is a well known low-activity Jupiter Family comet. Despite the low activity, we have witnessed outgassing activity in 1992, 2004, and 2012. In 2012 a broad tail-like feature (PA$\sim270^\circ, \sim2.3\times10^5$ km) and a narrow jet-like feature (PA$\sim180^\circ, \sim9.3\times10^4$ km) were seen simultaneously. Using Finson-...

Abstract We have investigated the influence of thin thermally opaque dust layers on the thermal emission of rocks and regolith and determined the thermal response of these dust-covered surfaces to diurnal insolation cycles. Results are computed for Hayabusa2’s target asteroid (162173) Ryugu, which was observed by thermal infrared instruments on the...

JAXA’s Hayabusa2 mission was launched in December 2014 to explore the pristine C-type asteroid (162173) Ryugu, whose bulk material can be considered representative for the volatile rich building blocks that formed the terrestrial planets. C-types are the most common variety of asteroids, and 75% of all known asteroids are of this type. They mainly...

The Rosetta observations have greatly advanced our knowledge of the cometary nucleus and its immediate environment. However, constraints on the mission (both planned and unplanned), the only partially successful Philae lander, and other instrumental issues have inevitably resulted in open questions. Surprising results from the many successful Roset...

Observations of the C-type NEA(162173) Ryugu by Hayabusa II demonstrated that this asteroid is a low-density rubble pile whose surface is dominated by large boulders. MASCOT’s[1] measurements during its operational phase on the surface of the rubble pile NEA (162173) Ryugu proided boulder brightness temperatures that allowed estimating thermal iner...

C-type asteroids are among the most pristine objects in the Solar System, but little is known about their interior structure and surface properties. Telescopic thermal infrared observations have so far been interpreted in terms of a regolith-covered surface with low thermal conductivity and particle sizes in the centimetre range. This includes obse...

Comet 49P/Arend-Rigaux is a well known low-activity Jupiter Family comet. Despite the low activity, wehave witnessed outgassing activity in 1992, 2004, and 2012. In 2012 a broad tail-like feature (PA∼270°,∼2.3×10^5 km) and a narrow jet-like feature (PA∼180°,∼9.3×10^4 km) were seen simultaneously. UsingFinson-Probstein (FP) dust dynamical models we...

Aims. We investigate the influence of the Yarkovsky force on the long-term orbital evolution of Jupiter Trojan asteroids. Methods. Clones of the observed population with different sizes and different thermal properties were numerically integrated for 1 Gyr with and without the Yarkovsky effect. The escape rate of these objects from the Trojan regio...

Numerical models are powerful tools for understanding the connection between the emitted gas and dust from the surface of comets and the subsequent expansion into space where remote sensing instruments can perform measurements. We will present such a predictive model which can provide synthetic measurements for multiple instruments (ROSINA, MIRO, V...

Aims. We investigate the influence of the Yarkovsky force on the long-term orbital evolution of Jupiter Trojan asteroids. Methods. Clones of the observed population with different sizes and different thermal properties were numerically integrated for 1 Gyr with and without the Yarkovsky effect. The escape rate of these objects from the Trojan regio...

The evolution of the temperature and porosity in potential parent bodies of Ryugu was calculated and compared with the measurements of MASCOT and properties of CI and CM chondrites. Key properties of the parent body were estimated.

On October 3rd, 2018 the Hayabusa2 spacecraft [1] delivered the MASCOT lander [2]to the surface of near Earth asteroid (162173) Ryugu,where it operated for 17 hours and 7 min. Ryugu has adiameter of 850-880 m, a geometric geometricalbedo between 0.045 ±0.002 at 0.55 μm and is classified as a Cbtaxonomic type[3]. During the surface mission, MASCOT i...

Correction to: Space Sci. Rev. (2019) 215: 2910.1007/s11214-019-0594-x The article The Thermal, Mechanical, Structural, and Dielectric Properties of Cometary Nuclei After Rosetta, written by Groussin et al., was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 2 May 2019 without open access. With th...

Knowledge of the surface temperature distribution on a comet’s nucleus and its temporal evolution at different timescales is key to constraining its thermophysical properties and understanding the physical processes that take place at and below the surface. Here we report on time-resolved maps of comet 67P/Churyumov–Gerasimenko retrieved on the bas...

Comets are made of volatile and refractory material and naturally experience various degrees of sublimation as they orbit around the Sun. This gas release, accompanied by dust, represents what is traditionally described as activity. Although the basic principles are well established, most details remain elusive, especially regarding the mechanisms...

The physical properties of cometary nuclei observed today relate to their complex history and help to constrain their formation and evolution. In this article, we review some of the main physical properties of cometary nuclei and focus in particular on the thermal, mechanical, structural and dielectric properties, emphasising the progress made duri...

Comets are made of volatile and refractory material and naturally experience various degrees of sublimation as they orbit around the Sun. This gas release, accompanied by dust, represents what is traditionally described as activity. Although the basic principles are well established, most details remain elusive, especially regarding the mechanisms...

On October 3rd, 2018 the Haya-busa2 spacecraft [1] delivered the MASCOT lander [2] to the surface of near Earth asteroid (162173) Ryugu, where itoperated for 17hoursand 7 min.Ryugu has a diameter of 850-880 m, a geometric V-band geometric albedo between 0.042 and 0.055, a bond albedo of 0.019±0.003, and is classified as a Cg taxonomic type[3]. Duri...

We have used the latest available shape model for gas and dust simulations of the inner coma of comet 67P/Churyumov-Gerasimenko for the period around May 2015 (equinox). We compare results from a purely insolation-driven model with a complementary set of observations made by ROSINA, VIRTIS, MIRO, and OSIRIS within the same period. The observations...

Aims. We use four observational data sets, mainly from the Rosetta mission, to constrain the activity pattern of the nucleus of comet 67P/Churyumov-Gerasimenko (67P). Methods. We developed a numerical model that computes the production rate and non-gravitational acceleration of the nucleus of comet 67P as a function of time, taking into account its...

Context. The change in rotation period and the orientation of the rotation axis of comet 67P/Churyumov-Gerasimenko (67P) can be deduced with high precision from images taken by the scientific imaging instruments on board the Rosetta mission. Non-gravitational forces are a natural explanation for these data. Aims. We describe observed changes in ori...

Aims. We use four observational data sets, mainly from the Rosetta mission, to constrain the activity pattern of the nucleus of comet 67P/Churyumov-Gerasimenko. Methods. We develop a numerical model that computes the production rate and non-gravitational acceleration of the nucleus of comet 67P as a function of time, taking into account its complex...

12 pages, 17 figures. Accepted for publication in forthcoming Rosetta issue of Astronomy and Astrophysics

Aims. We investigate the surface distribution of the source regions of dust jets on comet 67P/Churyumov-Gerasimenko as a function of time. Methods. The dust jet source regions were traced by the comprehensive imaging data set provided by the OSIRIS scientific camera. Results. We show in detail how the projected footpoints of the dust jets and hence...

The morphologic development of sublimating cometary surfaces is investigated in our study using analog laboratory experiments on Earth. The focus lies on the evolution of different morphologies, taking into account parameters such as the composition of the sample material and variable insolation flux. Different sample compositions and geometries ar...

Cometary surfaces are shaped through the process of activity when the comet approaches the sun and the sublimation of volatiles removes dust and gases. Recently, the ESA Rosetta mission showed the geomorphologic diversity of comet 67P/Churyumov-Gerasimenko in great detail (Fig. 1), giving us the opportunity to investigate the sublimation processes...

(Context) The change of the rotation period and the orientation of the rotation axis of comet 67P/Churyumov-Gerasimenko (67P/C-G) is deducible from images taken by the scientific imaging instruments on-board the Rosetta mission with high precision. Non gravitational forces are a natural explanation for these data. (Aims) We describe observed change...

Numerical models are powerful tools for understanding the connection between the emitted gas and dust from the surface of comets and the subsequent expansion into space where remote sensing instruments can perform measurements. We will present such a predictive model which can provide synthetic measurements for multiple instruments on board ESA's R...

We use the discrete element method (DEM) to numerically simulate the surface layer regolith dynamics of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) in order to infer mechanical properties of the surface material.

Between 2014 and 2016, ESA's Rosetta OSIRIS cameras acquired multiple-filters images of the layered nucleus of comet 67P/Churyumov-Gerasimenko, ranging from ultraviolet to near-infrared wavelengths. No correlation between layers disposition and surface spectral variegation has been observed so far. This paper investigates possible spectral differen...

From August 2014 to September 2016 ESA's Rosetta spacecraft escorted comet 67P/Chury-umov-Gerasimenko (hereafter 67P) on its journey into the inner solar system and out again. The mission provides, via various dust and gas instruments, unprecedented data on the nature of cometary activity. The determination of the activity distribution on the surfa...

We performed an investigation of a comet like porous surface to study how sub-surface sublimation with subsequent flow through the porous medium can lead to higher gas temperatures at the surface. A higher gas temperature of the emitted gas at the surface layer, compared to the sublimation temperature, will lead to higher gas speeds as the gas expa...

The previously defined regions on the nucleus of comet 67P/Churyumov-Gerasimenko have been mapped back onto the 3D SHAP7 model of the nucleus (Preusker et al., 2017). The resulting regional definition is therefore self-consistent with boundaries that are well defined in 3 dimensions. The facets belonging to each region are provided as supplementary...

Aims. Using data from the Rosetta mission to comet 67P/Churyumov–Gerasimenko, we evaluate the physical properties of the surface and subsurface of the nucleus and derive estimates for the thermal inertia (TI) and roughness in several regions on the largest lobe of the nucleus. Methods. We have developed a thermal model to compute the temperature on...

Asteroid (162173) Ryugu is the target object of Hayabusa2, an asteroid exploration and sample return mission led by Japan Aerospace Exploration Agency (JAXA). Ground-based observations indicate that Ryugu is a C-type near-Earth asteroid with a diameter of less than 1 km, but the knowledge of its detailed properties is still very limited. This paper...

We study various test scenarios that are aimed at the reproduction of different morphological features observed on comet 67P/Churyumov-Gerasimenko (hereafter 67P) and other small Solar system bodies. For this purpose, we simulate the surface layer regolith dynamics using the discrete element method (DEM). While the immediate objective is to calibra...

The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) onboard the European Space Agency's Rosetta spacecraft acquired images of comet 67P/Churyumov–Gerasimenko (67P) and its surrounding dust coma starting from May 2014 until September 2016. In this paper we present methods and results from analysis of OSIRIS images regarding the d...

The MASCOT radiometer MARA on board the Hayabusa2 mission will measure surface brightness temperatures on the surface of asteroid (162173) Ryugu in six wavelength bands. Here we present a method to constrain surface thermophysical properties from MARA measurements. Moreover, uncertainties when determining surface thermal inertia as well as emissivi...