By Anurag Sritharan
Our solar system is something we all learn from the second grade. First, we learn about the planets and moons, we then come across asteroids and comets, then move on to the Kuiper belt and finally the Oort cloud. Our satellites have sent us pictures from all the planets and many of their moons. So, we have a pretty good understanding of our solar system, right? The answer is a definite no. Scientists still discover objects in our immediate surroundings all the time. Space agencies such as NASA, ISRO, ESA, etc. have sent satellites to map and explore various planets and their moon. ISRO has its Mangalyaan 2 set to launch in 2024. But, JAXA’s latest ventures are now focused on asteroids and the abundant minerals they hold.
So, what exactly is an asteroid? As defined by NASA, “asteroids are rocky, airless remnants left over from the early formation of our solar system about 4.6 billion years ago” (Overview, NASA). This means that asteroids potentially hold large amounts of mineral deposits. In the 1950’s there were an approximate 20 to 30 known asteroids. Now, there are over 8 million in known existence. Asteroids are further categorized into 3 types based on the composition:
1. “The C-type (chondrite) asteroids are most common, probably consist of clay and silicate rocks, and are dark in appearance. They are among the most ancient objects in the solar system.
2. The S-types ("stony") are made up of silicate materials and nickel-iron.
3. The M-types are metallic (nickel-iron). The asteroids' compositional differences are related to how far from the sun they formed.” (In Depth, NASA)
Asteroids are also classified on the basis of their position in the solar system:
1. “Main Asteroid Belt: The majority of known asteroids orbit within the asteroid belt between Mars and Jupiter
2. Trojans: These asteroids share an orbit with a larger planet, but do not collide with it because they gather around two special places in the orbit.
3. Near-Earth Asteroids: These objects have orbits that pass close by that of Earth.” (In Depth, NASA)
Further research hinted that these celestial bodies could provide insight into the formation of our solar system giving us vital clues about how life on Earth came to be. The main aim of space research organizations is to figure out a way to tap that potential and help serve our needs in the fields of space research and industries. The first step is to map out all the asteroids and survey the surface for any signs of water or other minerals. After that scientists have to dig deeper into the surface and survey its core. Has this been done?
On December 3rd, 2014, Japan Aerospace Exploration Agency (JAXA) launched its Hayabusa 2 satellite with the main aim being to make a soft landing on Ryugu. The satellite reached Ryugu in June of 2018. On February 21st 2019 the satellite shot a metal projectile on the surface to try and collect samples from deeper in the asteroid and a soft landing was achieved twice to collect samples from the crater left by the projectile. It returned to Earth on 6th December, 2019, and landed somewhere in the deserts of Australia. “JAXA project manager Yuichi Tsuda told a separate news conference that he is starting to see “the end of the long journey.”” (Hayabusa2)
Asteroid Ryugu was discovered by the US LINEAR project on May 10th, 1999. The asteroid is a near Earth, ‘C’ type asteroid with a diameter of approximately 900m. The name of the asteroid has an interesting tale behind it that I would like to quote from the JAXA website
“The asteroid gained the name "Ryugu" in September 2015, nearly a year after Hayabusa2 was successfully launched in December 2014. The name was selected in a contest organized by JAXA, and is taken from the Japanese folk tale of Urashima Taro. In the tale, Urashima was a fisherman who rescues a turtle from a group of children. The turtle brings Urashima to an underwater palace known as "Ryugu" or "Dragon's Palace". He falls in love with a princess who begs him to stay, but after three days Urashima wishes to return to the surface. As a parting gift, the princess gives Urashima a box that she tells him never to open. Upon returning home, Urashima is shocked to find that 300 years have passed and everyone he knew has died. In confusion, he opens the box and is encased in a cloud of white fog. When the fog clears, he finds he is an old man, as the box contained his age.” (JAXA)
The satellite was powered by a Xenon ion drive which allowed it to orbit the asteroid. A closer look at the scientific payload of the satellite is crucial to understand how the mission was accomplished. Hayabusa 2 has three major Science payloads taken from the JAXA japan website (ミッション機器):
· Remote sensing: Optical Navigation Camera (ONC-T, ONC-W1, ONC-W2), Near-Infrared Camera (NIR3), Thermal-Infrared Camera (TIR), Light Detection and Ranging (LIDAR)
· Sampling: Sampling device (SMP), Small Carry-on Impactor (SCI), Deployable Camera (DCAM3)
· Four rovers: Mobile Asteroid Surface Scout (MASCOT), Rover-1A, Rover-1B, Rover-2.
The remote sensing devices are self-explanatory, they are used to capture various wavelengths of light. But, LIDAR had a more complicated role. A short ball covered with a reflective coating used as a marker was shot out from the satellite to the surface as a marker for the projectile as well as the rovers. They would receive and emit light from LIDAR to track its position in real-time and correct if any were required which was done by the Laser range finders equipped in LIDAR. The sampling devices were deployed in three stages: The First surface sample, the Sub Sampling stage and the second surface sample. The first two were carried out perfectly but the second sample surface was first postponed and then canceled due to an undisclosed error.
The two most important rovers were the MASCOT and MINERVA II which was split into MINERVA II-1 that contained both Rover-1A and Rover-1B and MINERVA II-2 or simply Roover-2. MASCOT was the only non-indigenous system on the mission and was contributed by German Aerospace Center. Both rovers were equipped with a large number of highly sophisticated scientific instruments that measured heat, took photos, acceleration, fine dust particle analyzer, communication equipment, etc.
Japan’s space research agency JAXA, well known for its advanced technology and rich culture, was inspired by origami to help fit its large payload in a tight space which is crucial for space travel. The solar panels in the satellite and rovers were used a specific folding pattern so that it can fit in the rocket and helps the panels deploy faster with less energy as it can builds kinetic energy while opening or unravelling by losing elastic potential energy. This technology is not a new concept and has been used in Indian satellites such as Chandrayaan 2.
Moving forward we may see a number of space agencies taking an interest in asteroids and sending missions to probe their surface and help further our understanding of these celestial objects and our solar system. JAXA’s success is a huge triumph and the first step in our endless thirst for knowledge about asteroids.
Work Cited
1. Overview, NASA Solar System Exploration . solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/overview/?page=0.
2. In Depth. solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/in-depth/.
3. Submission, Internal. Hayabusa2 Probe to Drop Ryugu Asteroid Capsule on Earth on Dec. 6. www.japantimes.co.jp/news/2020/07/15/national/science-health/hayabusa2-probe-ryugu-asteroid-2/.
4. ミッション機器: ミッション: JAXA はやぶさ２プロジェクト. www.hayabusa2.jaxa.jp/mission/m_payloard/.
5. Topics. www.hayabusa2.jaxa.jp/topics/20180404_e/.
Photos
6. Emily Lakdawalla, Charles H. Braden, and Loren A. Roberts for The Planetary Society - https://www.planetary.org/multimedia/space-images/spacecraft/hayabusa2-instrument.html
7. “Topics.” JAXA Hayabusa2 Project, www.hayabusa2.jaxa.jp/topics/20180404_e/.
8. “Oort Cloud Facts - Interesting Facts about the Oort Cloud.” Space Facts, 24 Apr. 2020, space-facts.com/oort-cloud/.