BepiColombo spacecraft is to conduct an Earth flyby in a few days.
Credit: ESA/ATG medialab

In a few days, the European Space Agency’s BepiColombo spacecraft is to conduct an Earth flyby before heading towards Venus – and in doing so the probe will scan the Moon using a unique instrument.

Earth’s Moon will be observed for the first time in the thermal infrared and examined for its mineralogical composition using the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) instrument. New information on rock-forming minerals and temperatures on the lunar surface is expected.

As early as April 9, with its Earth-facing side illuminated by the Sun, the Moon will be observed by the MERTIS instrument, developed and built by the German Aerospace Center (DLR) – the national aeronautics and space research centre of the Federal Republic of Germany.

The Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) instrument combines an imaging spectrometer with a radiometer, which is used for determining irradiance.
Credit: DLR (CC-BY 3.0)

One-of-a-kind opportunity

“Observing the Moon with our MERTIS instrument on board BepiColombo is a one-of-a-kind opportunity,” says Jörn Helbert from the DLR Institute of Planetary Research, who is a Co-Principal Investigator for MERTIS.

“We will examine the Earth-facing side of the Moon spectroscopically in the thermal infrared for the first time,” Helbert said in a DLR statement. “Without any absorption by Earth’s atmosphere, the view from space will provide a valuable new data set for lunar research. This is also an excellent opportunity to test how well our instrument works and to gain experience in preparation for operations in Mercury orbit.”

Intensive preparations

MERTIS has two uncooled radiation sensors. Its spectrometer covers a wavelength range from seven to 14 micrometers, and its radiometer to a wavelength range from seven to 40 micrometers. It will identify rock-forming minerals in the mid-infrared at a spatial resolution of 500 meters.

“I am anticipating many exciting results from the observations with MERTIS. After about 20 years of intensive preparations, the time will finally come on Thursday – our long wait will be over, and we will receive our first scientific data from space,” explains Harald Hiesinger from the University of Münster, Principal Investigator for the MERTIS experiment.

Schematic representation of BepiColombo’s Earth flyby on April 10, 2020.
Credit: DLR, based on an ESA model

Good planning

MERTIS will observe the Moon from distances of between 460,000 miles (740,000 kilometers) and 422,532 miles (680,000 kilometers) for four hours, explains Gisbert Peter, MERTIS Project Manager at the DLR Institute of Optical Sensor Systems.

“Having the Moon in the spectrometer’s field of view before the flyby is partly an astronomical or geometric ‘coincidence’ and, above all, due to good planning,” Peter added.

Six year journey

The main purpose of the Earth flyby is to slow down BepiColombo somewhat without expending propellant, in order to bring the spacecraft onto a trajectory towards Venus.

With two subsequent close flybys of Venus (the first flyby will take place on October 16, 2020), BepiColombo will then be on a trajectory that will take it to the final destination of the six-year journey, an orbit around Mercury, the innermost planet of the Solar System.

BepiColombo was launched on 20 October 20, 2018 by an Ariane 5 launch vehicle.

 

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