Ended prematurely mission of Japanese research satellite Hitomi proves that even short scientific space mission could bring important discovery. Before its failure on March 26, 2016, Hitomi managed to gather significant data using its scientific payload.
Who dares wins – this should be new motto for Japan Aerospace Exploration Agency. Developing mission of Hitomi satellite (known also as Astro-H) was great challenge for JAXA in technical dimension. Astro-H was designed by JAXA engineers as X ray telescope for deep space observation. With advanced deployable X ray telescope and various scientific devices it was big chance to improve knowledge on deep space. It was also kind of advertisement of technical skills of JAXA. Launched on atop of H-IIA rocket on February 17, 2016, for 3 years mission, satellite failed after 40 days of operating. During flight on designated orbit with inclination at 31.01° (perigee at 559.85 km, apogee at 581.10 km) on March 26, 2016 satellite lost communication and failed due the human error in software of onboard computer. Inertial reference unit (IRU) responsible for stability of the flight, wrongly interpreted data and put satellite into spinning movement; rotating speed caused literally disintegration of the Hitomi. JAXA was trying to resume contact with satellite, but on April 28, 2016 they were forced to announce that mission became failure. Mission, which cost $290 million ($70 million was covered by NASA), seemed to bring nothing new to deep space astronomy until July 6, 2016.
One of the most important NASA research centers, Goddard Space Flight Center in Greenbelt, Maryland, announced about spectacular discovery made by Hitomi before March 26 incident. One of the onboard instrument, Soft X-ray Spectrometer (SXS-designed and manufactured in Goddard SFC) gathered first detailed data in history about Perseus galaxy cluster. Galaxy cluster is form of multiple celestial bodies formed in number of galaxies hold together by gravity force of dark hole. Perseus is 240 million light years away from Earth; space inside Perseus was known as filled with extremely hot gas with assumed temperature of 50000000°C. But nature, structure and dynamics of this gas were unknown because lack of appropriate instrument for measurements. SXS which was operating in X ray, was able to took detailed measurements of gas and transmit them to Earth. After analysis of gathered data it was discovered that in spite of great gravity inside Perseus gas dynamics seems to be low in deep space scale. Velocities are oscillating around 560000 km /h (comparing to millions of light years which are separating Earth from Perseus is in fact low value). During two and half day of observation SXS measured values inside designated squared zone in Perseus with dimensions of 195000 IAU x 195000 IAU ( to remind on light year is equal to 9 trillion kilometers). According to Brian McNamara, a professor of physics and astronomy at the University of Waterloo, gas inside Perseus is absorbing energy from dark hole very fast what results in its low velocity and motion: only 4% of gas inside patch was in turbulence. These data will improve knowledge on galaxy clusters and will help in future research on Milky Way. According to Brian McNamara:
“Hitomi’s Perseus observation tells us that we can probably weigh distant galaxy clusters to greater accuracy than we can weigh our own Milky Way galaxy.”
Discovery of low dynamic of gas inside Perseus shows how promising was mission of Astro-H, if only during first month of mission such important scientific discovery was made. In spite of structure and dynamics of gas, data from SXS also helped in discovering composition of Perseus. Analysis of X ray spectrum showed presence of iron, nickel, chromium and manganese what indicates material of stars which exploded as supernovae in history of Perseus.
Discovering these facts was possible only with Hitomi satellite; of course this mission would be more helpful if would last assumed three years; it is sad truth that experience is necessary element of space exploration. The more we should look with great respect for JAXA enthusiasm for taking most ambitious challenges against the risks which this entails.