| Space

German scientists present proposals for exploring Apophis

Close flyby of Earth
AI-generated artist's impression of Apophis during its close flyby of Earth (not to scale!).

DLR with assistance from perchance.org

In five years, asteroid Apophis will fly very close to Earth. In this case, 'close' means not only within the geostationary orbit where most telecommunications satellites are located, but also that it will even be visible to the naked eye. This close flyby offers a unique opportunity for the scientific study of an object of this type.

Researchers are particularly keen to investigate the effects that 'tidal forces' caused by Earth will have on the asteroid during its flyby. It is thought that they could change the physical and dynamic state of the celestial body, which in turn would allow scientists to draw conclusions about its structure. Tidal forces could also change the rotation of Apophis. Such information would prove essential if one day it were necessary to divert such a body from a collision course with Earth.

In my last DLR blog post (Serendipitous science from asteroid Apophis' Earth near miss), I reported on the international scientific coordination workshop Science@Apophis, which took place in February of this year at DLR in Cologne. Some initial proposals for the scientific investigation of Apophis were made there, and we recently had the Apophis T-5 Years workshop at the European Space Research and Technology Centre (ESTEC) in Noordwijk in the Netherlands. Among other things, the payload concepts presented in February were presented in greater detail and discussed with the global scientific community. Around 250 engineers and scientists took part in the workshop, and more than ten mission concepts for Apophis and even more payloads were presented during the two-day gathering.

In this blog post, I will set out the proposals from the German scientific community for individual research on Apophis. I will not go into too much detail but will link to the relevant detailed 'extended abstracts' for those interested in the technical and scientific particulars. Unlike a standard abstract, which summarises the research and development work in a single paragraph, detailed abstracts are written in the style of a research paper, including references, figures and tables, but are limited to a few pages in length (two pages for the Apophis T-5 Years Workshop).

Visit to the European Space Research and Technology Centre (ESTEC)
Group picture of scientists and engineers from all over Europe and further afield during a visit to the Hera space probe at the European Space Research and Technology Centre (ESTEC). Hera is ESA's first planetary defence mission and is scheduled to launch to the Didymos binary asteroid system in October.


Before I discuss the individual payloads proposed, I would like to highlight three proposals at a mission level. In other words, these could be part of a larger mission as a daughter satellite or lander deployed from a mother spacecraft.

Proposals for a lander, CubeSats and sample return as additional mission elements

The MASCOT (Mobile Asteroid surface SCOuT) lander (see this DLR blog post) was built by DLR in Bremen and successfully deployed on the surface of the Ryugu asteroid by its Japanese mother probe, Hayabusa2, in 2018. This development led to a proposal for a MASCOT3 lander that would deliver dedicated scientific instruments for measurements on the surface of Apophis. The inclusion of such a lander in an orbiting space probe mission would provide a valuable addition to the data obtained from orbit by combining local in-situ data with global remote sensing data. You can find more information in this abstract.

Following the example of ESA's Hera mission, a mission to Apophis could also deploy CubeSats in deep space – these shoebox-sized satellites are only released from their mother vessel when they arrive at the target asteroid. This proposal fits very well with the German government's new space strategy, which explicitly supports the use of small satellites for space research. For more information, including possible payloads for the CubeSat (see below), see this abstract.

A highly ambitious but scientifically promising idea is the proposal to bring a sample of Apophis back to Earth for more detailed study in terrestrial laboratories (abstract). While travelling to an asteroid is difficult enough, returning a sample requires a return flight as part of the mission, making it even more complex. In this case, however, the sample could 'hitchhike' back to Earth. Landing on Apophis before the close flyby would make returning to Earth relatively easy, as it would simply be a matter of 'jumping off' Apophis shortly before it passed close to our planet. This summary outlines the technical concept and scientific motivation behind the sample return.

The University of Würzburg team
The University of Würzburg team in front of their conference poster, presenting their work on a potential German CubeSat contribution to the study of Apophis

University of Würzburg

Scientific payload proposals range from cameras to magnetometers and plasma spectrometers

In addition to these three mission-level contributions, several potential payload contributions were also presented at the workshop. A payload is a scientific instrument or experiment that provides scientific data. In most cases, a mission carries more than one payload, collectively called a payload suite, with each measuring different physical properties of a celestial body.

The payloads proposed at the workshop were a radar, a magnetometer, a plasma spectrometer, various types of cameras and a radiometer. A brief overview:

  • The above CubeSat proposal (abstract) envisages the use of three payloads. The first is a magnetometer to measure a possible magnetic field around Apophis, but also the plasma interaction during Apophis' immersion in Earth's magnetosphere. The other two payloads considered for the CubeSat (and other scenarios) were a radar and a camera, which are presented below.
  • The CubeSat, or a lander, could be equipped with a small camera. The MASCam, a wide-angle camera, flew on the MASCOT lander as part of the Hayabusa2 mission and took images during its descent to the asteroid surface, providing contextual information for the instruments on MASCOT. Building a payload typically involves constructing two identical instruments: the flight model (FM) is designed for the flight into space, and if there are any last-minute problems with the FM, the flight spare (FS) is usually provided. This is an exact copy of the FM, enabling it to be replaced if necessary. The MASCam FS still exists and could itself be used. You can find further details of this camera in the abstract.
  • A radar could be installed not only on the CubeSat, but also on a lander or the main spacecraft. Radar can be used to learn more about the inner structure of an asteroid. The abstract for the radar also explains the difference between monostatic and bistatic modes; monostatic mode applies to a single spacecraft, while bistatic mode uses two spacecraft, each carrying a radar device. Of course, the more the merrier. A 'multi-static' configuration with a radar on more than two spacecraft or landers would provide even more detail about the interior of the asteroid.
  • Similar to the magnetometer, the proposed plasma spectrometer would analyse the interaction of the plasma in Earth's magnetosphere as Apophis plunges into it, measuring the interaction between the asteroid surface and the plasma and enabling researchers to determine the distribution of electrons and ions. As outlined in this abstract, an FS of the Jovian Electron and Ion Sensor (JEI) from PEP (the Particle Environment Package) remains available from ESA's Jupiter mission, JUICE. Although the plasma environments on Jupiter and Earth are different, the measurement principle remains the same. An Apophis mission would have one advantage over the Jupiter mission: the shielding materials that protect the sensor from the very high radiation on Jupiter would not be necessary on Apophis, allowing for a reduction in the mass of the instrument. More details about this unique scientific case of space plasma physics were presented in this abstract.
  • The Framing Camera on the Dawn mission provided amazing images of the dwarf planet Ceres and the asteroid Vesta. This workshop abstract suggested using the camera's FS for a mission to Apophis. The fact that the camera has seven colour filters that cover the 0.4 to 1.0 micrometre wavelength range makes it a particularly enticing prospect from a scientific point of view. These filters could be used to obtain spectral information in addition to the usual images, thereby allowing the composition of Apophis to be determined with greater precision.
  • Last but not least, this abstract proposed performing surface measurements in thermal infrared wavelengths. With the help of a radiometer, scientists would be able to discern the thermophysical properties and porosity of the surface material, along with the influence of the dust environment. Porosity is a measure of the empty spaces inside a solid material – the proportion of voids in an enclosed volume. One challenge is that the equipment has to land on Apophis and ideally survive for a day and a night – about 30.5 hours – in order to get scientific results.

Other German proposals that were not featured in their own poster at this event included contributions to radio science (to determine Apophis' gravity field), a laser altimeter (to reconstruct the shape of Apophis and possible changes during the flyby), a Mössbauer spectrometer (a contact instrument to measure the composition of the surface material) and the Asteroid Framing Cameras (AFCs, one of the German contributions to the ESA Hera mission which enable navigation around Apophis and the scientific study of asteroids).

Various proposals for researching Apophis
A collage of the posters presented at the Apophis T-5 Years Workshop, including the abstracts mentioned in this blog post



Overall, the Apophis T-5 Years workshop was a great success, giving the international scientific community the opportunity to discuss not only the proposals presented in this DLR blog post, but also many more ideas for the scientific study of Apophis when it flies by Earth in 2029.

Discussions will continue in September, when the largest planetary science conference, the Europlanet Science Congress (EPSC), comes to Berlin. This will be a wonderful opportunity for scientists to present their work and a great chance for both undergraduate and postgraduate students, educators and amateur astronomers to learn a great deal about planetary science and Apophis itself. Don't miss this other important home game on our doorstep in Berlin – we hope to see you there!

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