Various studies related to space and planets are carried out at the School of Science.
The universe hides many secrets yet to be revealed to mankind.
◎Challenging the mysteries of the 11-year solar cycle<Solar and Astrophysical Plasma Physics>
Associate Professor Takaaki Yokoyama, Department of Earth and Planetary Science
Sunspots observed on the surface of the Sun appear as dark spots because the temperature is lower than the surrounding areas. They are regions of strong magnetic field caused by concentrations of magnetic flux emerged to the solar surface. The number of sunspots on the solar surface has been recorded ever since Galileo first started observation of solar activities in around 1600. Sunspot counts are known to vary according to the 11-year solar cycle. However, no one has yet explained why there are cycles in solar activity.
A team led by Associate Prof. Yokoyama and Dr. Hideyuki Hotta, a graduate of the Yokoyama Lab and an Assistant Professor of Chiba University, took on the challenge to unlock the mysteries of the solar cycle. They revealed how the magnetic fields (sunspots) are generated through the world’s highest resolution simulations by using the RIKEN K computer.* The figures below show the turbulent flow (above) and magnetic field (below) obtained by numerical simulations. It also shows how large-scale ordered magnetic fields are being generated from highly chaotic and turbulent environments.
The Yokoyama Lab also engages in observational and theoretical studies of astrophysical plasmas.
*This research was published in Science on March 25, 2016 (VOL. 351).
◎Searching for signs of an atmosphere on Mars <Evolution of Planets, Astrobiology>
Associate Professor Yasuhito Sekine, Department of Earth and Planetary Sciences and Department of Earth and Planetary Environmental Science
This is a photo of Curiosity exploring a crater on Mars. Scientists believe that there used to be a lake in the crater. Ferric and manganese oxides have been found from analysis of the layer of mud and sand deposited at the bottom of the lake, which suggests the possibility that Mars once had an atmosphere containing oxygen.
The Sekine Lab studies the birth and evolution of planets and satellites, including Earth, both within and outside of the solar system. They are particularly interested in the process of how life-bearing environments, in other words atmospheres and oceans, were formed on planets and satellites where life exists or may potentially exist. Specifically speaking, early Earth, Mars, Jupiter II Europa, Saturn VI Titan, Saturn II Enceladus and other planets and satellites outside of the solar system are the targets of their studies.
The main approaches the Sekine Lab adopts are laboratory chemical experiments, fieldwork and sample analysis. It is necessary to understand how the elements that constitute atmospheres and oceans are metamorphosed during the activity of planets and satellites in order to know the origins of environments that can accommodate life. They also combine numerical calculations to elucidate the mysteries of planetary evolution.
◎Understanding the accelerating expansion of the universe from a supernova explosion <Observational Cosmology, Extra-Galactic Astronomy, Supernova>
Professor Mamoru Doi, Institute of Astronomy, School of Science
The three small photos on the right show a supernova explosion captured on April 3, 2016 using the HSC/Subaru Telescope installed on top of Mauna Kea in Hawaii. The photos show, from left to right: about 12 hours after the explosion, one day after the explosion, and a follow-up observation about one month after the explosion (the bright dot at the tip of the red arrow is the supernova). The left and middle photos were taken with the wide-field Hyper Suprime-Cam mounted on the Subaru Telescope and the one on the right was taken with another telescope on Mauna Kea. We succeeded in capturing this supernova explosion at a very early stage, earliest among previous observations of this type of supernovae, and found that the big explosion came after a small explosion that occurred at a very early stage of the process.* Ji-an Jiang, a second year doctoral student of the Doi Lab, played a central role in the discovery.
The image below the photos is an illustration of the explosion. It is thought that the accumulated helium on the surface of the white dwarf was ignited, causing a helium nuclear explosion. Shock waves generated by this precursor event propagated inward, eventually igniting the whole star in a nuclear burst.
A supernova explosion is one of the brightest events in our universe. Because of the uniform and extremely high brightness, they are widely used as the standard candle for distance measurement in astronomy. This was also used in the discovery of the accelerating expansion of our universe. The Doi Lab also studies dark energy, which is thought to be the cause of this mysterious accelerating expansion.
*This research was published in Nature on October 5, 2017 (Vol. 550).
Interview and text: Masatsugu Kayahara
Originally published in The School of Science Brochure 2018