A once-in-a-millennium event: Asteroid Apophis passes Earth ESA mission involving TU Braunschweig to monitor the flyby at close quarters

When the asteroid Apophis flies past Earth on 13 April 2029, a magnetometer developed at Technische Universität Braunschweig will carry out geophysical measurements directly on its surface. The MARIE instrument is part of a landing CubeSat from the ESA’s RAMSES mission and, together with other experiments, is set to investigate the effects of this exceptionally close flyby of Earth. The rare flyby of a 340-metre-wide asteroid offers a unique scientific opportunity to study the properties of near-Earth asteroids and their interaction with Earth’s magnetosphere. TU Braunschweig is thus making a significant contribution to one of the most spectacular international space missions of the coming years.

The asteroid Apophis will not collide with Earth on Friday, 13 April 2029 – fortunately, as Apophis has a diameter of 340 metres. In terms of diameter, it is five times smaller than the meteorite that formed the Nördlinger Ries 15 million years ago, but also 18 times larger than the meteorite that fell in Chelyabinsk, Russia, in 2013, causing the most powerful meteorite impact of the past 100 years.

Apophis will pass the Earth at a distance of around 32,000 kilometres, which is roughly one-tenth the distance to the Moon. Its trajectory is now known to an accuracy of ±3 kilometres, so a collision that would result in the devastation of an entire continent can be ruled out.

An event that occurs only once every 7,000 years

Statistically, such a close fly-by of such a large asteroid occurs only about once every 7,000 years. It therefore offers a unique opportunity to study asteroids with orbits similar to Earth’s, and to develop defence strategies for smaller, as yet undiscovered asteroids as well.

Earth defence programmes

All major space agencies have launched Earth defence programmes. The European Space Agency’s (ESA) Space Safety Programme encompasses not only protection against near-Earth objects but also the forecasting of space weather driven by solar activity, as well as the protection of active satellites from man-made space debris.

As part of these programmes, numerous proposals have been drawn up to monitor Apophis before, during and after its flyby of Earth. The ESA, in collaboration with the Japan Aerospace Exploration Agency (JAXA), is carrying out an extremely spectacular mission. The European space probe RAMSES, which is to be launched on a Japanese launch vehicle one year before Apophis’s flyby, is to be steered into the asteroid’s orbit in order to observe its flyby of Earth at close quarters.

The Earth’s tidal forces will cause the asteroid’s surface to change during the flyby, and rocks may break away from the surface. However, these processes will not be observed by RAMSES alone. In addition, two small sub-satellites (CubeSats) will detach from RAMSES prior to the flyby. One of these two CubeSats is set to land on the surface of Apophis, monitor the flyby from this vantage point and carry out geophysical measurements using three instruments.

It is remarkable that the ESA, together with the European space industry, the national space agencies and scientific institutes, is able to carry out such a challenging mission in an exceptionally short time – at a pace reminiscent of the pioneering years of space exploration.

Magnetometer from TU Braunschweig on a microsatellite

Thanks to the dedicated efforts and funding provided by the German Space Agency at the German Aerospace Centre (DLR), with funds from the Federal Ministry of Research, Technology and Space (BMFTR) following a resolution by the German Bundestag, two German experiments will also contribute to the exploration of Apophis as part of the national ‘Space Exploration’ programme. The Max Planck Institute for Solar System Research in Göttingen will contribute the RAMSES Plasma Spectrometer (RPS), whilst the Technical University of Braunschweig will be represented by a magnetometer on the landing CubeSat.

The MARIE (Magnetosphere-induced Apophis Response Investigation Experiment) magnetometer, developed at the Institute of Geophysics and Extraterrestrial Physics, is based on instruments that have already been successfully deployed on other landers. Similar measurement systems were used as early as 2014 on the comet Churyumov–Gerasimenko and in 2018 on the asteroid Ryugu.

Observing with your own eyes

A distinctive feature of Apophis is that the asteroid will pass through Earth’s magnetosphere and outer radiation belt. The plasma spectrometer and magnetometer therefore offer a unique opportunity to study the interaction of such a large body with Earth’s plasma environment.

This once-in-a-millennium event will, for the first time, enable around two billion people to observe an extraterrestrial object near Earth with their own eyes. Like a bright satellite, Apophis will be visible in the evening sky, appearing from the south-east and passing over Europe and Africa.

“We scientists at TU Braunschweig are very proud to be able to monitor this extraordinary event from Apophis’s perspective. The landing of a German instrument from TU Braunschweig on Apophis will be something very special for all of us,” says Professor Ferdinand Plaschke, Head of the Institute of Geophysics and Extraterrestrial Physics.