On Wednesday, June 27, the automatic interplanetary station Hayabusa-2, after a four-year space trip, finally arrived at its target – an asteroid 162173 Ryugu. The next year and a half, she will spend in the vicinity of this asteroid, studying it both from the orbit, and with the help of the descent module. It is assumed that the station will take the soil, which in five years will be delivered to Earth in a sealed capsule. Editors N + 1 decided to understand how the main stage of the mission will pass and what a small, unattractive celestial body in orbit between Earth and Mars so interested scientists.
How the Solar System was born and how life originated in it – these two questions have long been of interest to scientists. Over the last decade, our ideas about the formation and evolution of planetary systems have been greatly enriched by observing other star systems, both already formed and just being born. However, in addition to physical processes, which understand models that are built on the basis of observable data, researchers are interested in “chemistry” – how can the composition of the planets and their atmospheres and how it depends on the place of formation of the planet and on the age and composition of the star.
In the case of our planetary system, an understanding of chemical processes can help answer the question of how our Earth and other planets were formed, and where from it appeared “building materials” for the emergence of life, such as water and organic matter.
“Chemistry” of planetary systems can be studied differently – remotely, by spectroscopic analysis of radiated or absorbed light by atmospheres or surfaces of planets or protoplanetary disks, or by studying the matter left after the formation of the planets. It is very difficult to find it, especially in its original form (ie, not subjected to differentiation processes, strong heating and chemical composition changes) in the modern Solar System – too much time has passed since its formation. Nevertheless, it is possible – the particles of the protosolar nebula can be found in the so-called “primitive” bodies – small asteroids or comets formed on the outskirts of the solar system, as well as in meteorites such as chondrites falling on the Earth.
From the point of view of chemistry, the elemental composition of such meteorites is close to the composition of the Sun, and the age is estimated at more than 4.5 billion years, which almost corresponds to the age of our planetary system. However, on Earth there is a danger of contamination of meteorite substance (and strong heating during flight through the atmosphere can negatively affect the composition). As for the composition of the small bodies of the solar system, its study with the help of onboard means of interplanetary stations does not always help to fully disclose all the riddles of the “chemistry” of planetary systems. Therefore, researchers are interested in the possibility, in terrestrial conditions, to work with matter directly delivered from asteroids and comets.
This is the main goal of the Hayabusa-2 mission : to bring to earth scientists earth samples from the C-class asteroid, which are considered to be one of the most ancient bodies of the Solar System and a source of meteorites such as carbonaceous chondrites . We did not accidentally say “the main” – in fact, the mission at once two. In addition to scientific research, Japanese researchers are also interested in the purely practical task of developing the technology of the returned automatic interplanetary missions and technologies for industrial development and development of the asteroids in the solar system that can be developed in the future with manned flights to the outer space.
To learn more about the origin and evolution of the solar system, it is necessary to investigate different types of asteroids , and then conduct their comparative analysis. The Hayabusa-2 predecessor, the mission of Hayabusa(or MUSES-C), which worked in 2003-2010, explored the near-Earth asteroid of the Itokawa S-Class (25143) and for the first time in history successfully delivered a sample of its soil to Earth, despite the setbacks , chasing the station – one of the ionic engines and two of the four flywheels in the orientation system failed, the descent module instead of landing on the surface of the asteroid jumped from it and flew back into space, and both attempts to take ground were malfunctioned. Nevertheless, the station fulfilled its task, and engineers received a harsh but necessary experience.
However, there is an even more ancient, widespread and interesting type of asteroids – the C-class , which is characterized by an increased content of carbon-containing or hydrated minerals and can contain the untouched substance of the protosolar nebula. Asteroid of a similar class (162173) Ryuga and was chosen as the target. It was opened as part of the LINEAR project in May 1999 and is part of a group of near-Earth asteroids such as Apollo. Its orbit has an elongated shape and crosses the orbits of the Earth and Mars, and the diameter is estimated at about 900 meters.Radar observations showed that the shape of the asteroid 162173 Rjugu is close to spherical, and the albedo of the surface is very low. The asteroid’s orbit was suitable to allow the spacecraft to visit it and then return to Earth, which was the second decisive criterion in choosing the target for Hayabusa-2.
Journey to the asteroid Ryuga began on December 3, 2014, when the launchvehicle H-IIA was launched from the Tanegashima launch site , which launched Hayabusu-2 into space. In total, the device flew 3.2 billion kilometers, although the encounter with the asteroid occurred only 280 million kilometers from Earth.
Such a long trajectory is explained by three orbits around the Sun, during which the device successfully completed a gravitational maneuver near the Earth in 2015 and three periods of speed dialing with the help of its ionic engines to catch up with the asteroid and enter orbit around it. At the beginning of June 2018, three thousand kilometers from Ryuga, the station switched off its propulsion system and began the approach phase to the asteroid, which included obtaining navigational shots and nine trajectory corrections.
When Hayabusa-2 approached the asteroid for 2100 kilometers, a painstaking search was started for possible small satellites of Ryuga-an important task not so much for science as for the safety of the apparatus. Due to the small size of the Ryuga, its sphere of Hill (the area on which its gravitational influence extends) extends to a distance of up to 90 kilometers. Satellites were not found, but the presence of bodies with a diameter of less than 50 centimeters is not excluded, so the search in the future can be repeated.The closer the station reached the asteroid, the more interest the team of engineers and scientists grew in it. The first fairly clear pictures showed that the estimates of the diameter of the Ryuga (about 900 meters) and the period of its rotation around its axis (7.5 hours), made on the basis of ground-based observations, proved to be correct. Estimates of the shape as the station approached Ryuga were constantly changing – at first the asteroid seemed similar to the Japanese pel’meni of Dango, then to a cube and finally to a fluorite crystal. Together with the form, the surface details became even more visible: large craters (the largest has a diameter of about 200 meters) and depressions, boulder groups on the surface, the equatorial ridge, and a 150-meter rockat the north pole of the asteroid. It turned out that the rock on the pole and the equatorial ridge look much brighter than the surrounding surface, which can tell about the differences in the mineral composition.
All this testifies to the fact that Ryugu passed a complex evolutionary path and could have formed when a larger object was destroyed. The axis of rotation of the asteroid is almost perpendicular to the ecliptic plane, and the direction of its rotation has a retrograde character, that is, opposite to the direction of rotation of most planets and the Sun in our system (except for Venus and Uranus, which also rotate “in the wrong direction”).Now the station on a stable 20-kilometer orbit around the asteroid, and all systems are operating in normal mode. The signal from it to the Earth reaches in 15 minutes. The rest of the summer “Hayabusa-2” will devote to the study of Ryuga and its gravitational field from the orbit, approaching the asteroid to a distance of one kilometer. In early October, it is planned to land the MASCOT landing vehicle and one or more of the MINERVA-II landing modules for the first time on the surface of the asteroid, then, at the end of the year, there will be a period of radio silence during which the Sun will interfere with communication with the station.
In January 2019, the work of the station will resume. It is planned to carry out several more encounters with Ryuga, as well as to shoot on its surface with a special device, through which researchers will be able to take a sample of the subsurface layer of the asteroid.
In November-December 2019, the station will lie on the reverse course to Earth and drop the capsule with the substance of the asteroid into the atmosphere in December 2020.
The scientific arsenal, with which the apparatus will study an asteroid, is quite extensive. It includes an optical system ONC (Optical Navigation Camera), consisting of a camera with a long focus lens and two – with short focus, allowing you to receive both navigational images that help in correct orientation of the apparatus and correction of its trajectory, as well as images of the surface of the asteroid. Another station is equipped with an infrared camera TIR (Thermal Infrared Camera), designed to determine the surface temperature of the asteroid in various areas and its thermal inertia . A large difference in surface temperatures in the illuminated and night areas will indicate a more loose or finely dispersed soil.
The payload also includes an infrared spectrometer NIRS3 (Near-infrared spectrometer) designed to search for water ice and determine the chemical composition of the Ryu поверхности surface, as well as a laser altimeter and four descent modules: MASCOT ( Mobile Asteroid Surface Scout ) and three small MINERVA-II, which will be dropped from the side of the orbiter during rapprochement with the asteroid. They are designed to study the physical and chemical properties of the surface.
The soil will be taken using several tools as follows. In the beginning, Hayabusa-2 will approach the surface of the asteroid and shoot at the height of 500 meters with a penetratorSCI (Small Carry-on Impactor), consisting of a copper projectile weighing 2.5 kilograms and 4.5-kilogram charge of explosive. It is assumed that the projectile will hit the surface of Ryuga at a speed of two kilometers per second, the explosion will be observed by the DCAM3 camera. Impact crater will become a place for further research of the orbiter, which will first explore the exposed sub-surface layers of the remote, and then draw near and with the help of a special device will take soil samples from the crater. Then the sample will be placed in the capsule returned to the Earth. The place of discharge of the penetrator, as well as the places where the modules were dropped, has not yet been determined, this will be the subject of further discussions among the mission team.
“Hayabusa-2” is not the first or the last project to study the soil of small bodies of the Solar System. In July 2005 such a bombardment of the surface of the comet 9P / Tempel was carried out by the Deep Impact spacecraft , however, then the ground was not taken, and all observations were remote. In 2006 the descent capsule of the interplanetary station returned to Earth “Stardust” , which carried in itself the coma particles of the comet 81P / Wild , enclosed in an airgel. And next year the OSIRIS-REx spacecraft should reach the asteroid Bennu and get a sample of its soil, which it will deliver to Earth by 2023.