16-Feb-2022: Atmospheric pressure on surface of Pluto is more than 80,000 times less than Earth: study based on observation from Devasthal observatory
A team of scientists, including Indian and International collaborators, have derived the accurate value of Pluto’s atmospheric pressure at its surface. It is more than 80,000 times less than the atmospheric pressure at mean sea level on Earth.
The pressure was calculated from data obtained by observation of stellar occultation by Pluto on 6 June 2020 using 3.6-m Devasthal optical telescope (DOT) (India’s largest optical telescope) and 1.3-m Devasthal Fast Optical Telescope (DFOT) telescopes located at Devasthal, Nainital.
In astronomy, an occultation happens when a celestial object gets hidden from the view of the observer due to another celestial object passing in between them. A compilation of twelve stellar occultations by Pluto observed between 1988 and 2016 showed a three-fold monotonic increase of atmospheric pressure during this period.
An international team of scientists, including members from Aryabhatta Research Institute of Observational Sciences (ARIES), used signal-to-noise ratio light curves obtained from the sophisticated instruments used in the observations to derive an accurate value of Pluto’s atmospheric pressure at its surface. It was found to be 12.23 μbar -- 80,000 times less than the atmospheric pressure at mean sea level on Earth. They also found that the pressure at the surface is close to the seasonal peak of Pluto.
The research published in ‘Astrophysical Journal Letters (ApJL)’ showed that since mid-2015, Pluto’s atmosphere is in a plateau phase close to peak and is in excellent agreement with the model values calculated earlier by the Pluto volatile transport model in 2019. The team explained further that this occultation was particularly timely as it can test the validity of the current models of Pluto’s atmosphere evolution.
The study also confirms earlier findings that Pluto suffers intense seasonal episodes because of large depression on Pluto, known as Sputnik Planitia. Pluto’s poles remain, for decades, in permanent sunlight or darkness over its 248-year long orbital period leading to strong effects on its Nitrogen (N2) atmosphere that is mainly controlled by vapour pressure equilibrium with the surface N2 ice. Moreover, as Pluto is now moving away from the Galactic plane as seen from Earth, stellar occultations by the dwarf planet are becoming increasingly rare, making this event a decisive one.
28-Jan-2022: Students & scientists from various parts of India and USA discuss characterizing space radiation environment
Domain experts and students from India and the USA discussed issues ranging from characterizing the space radiation environment to astrobiology and the application of artificial intelligence and machine learning tools in it at the Indo-US Workshop on "Space Radiation Workshop: Radiation Characterization from Sun to Earth, Moon, Mars and Beyond" held from 24 – 28 January 2022.
Shri Kiran Kumar, former chairman, ISRO, gave an overview of previous space missions by India and chalked a roadmap of new missions till 2025 in his keynote address on Jan 26, 2022. He highlighted how ISRO started with humble beginnings with limited resources and talked about some of the notable space missions by ISRO.
He said that Chandrayaan 1 was a significant mission for ISRO, and it changed the perception of the Moon for us, including discovery of OH and water molecules on the Moon. "Mars Orbiter Mission has completed 7 years studying Mars. AstroSat mission is the first dedicated astronomical observatory that India has put in orbit. It is a large collaboration between many national institutes and has provided data for a large number of important studies in astronomical research. Chandrayaan 2 orbiter is healthy, and all payloads are operational. The spacecraft can remain functional for many more years. The data obtained till now has already resulted in many publications," he added. He also pointed out that the making of the satellite for the Aditya-L1 mission, which will study the sun, is nearing its completion and will likely be launched this year. He also said that in future, ISRO and the Japan Aerospace Exploration Agency (JAXA) will be collaborating on a lunar exploration mission.
The workshop was supported by the Indo-US Science and Technology Forum and hosted by the Aryabhatta Research Institute for Observational Sciences (ARIES), Nainital, an autonomous institute under the Department of Science & Technology, Govt. of India) and Indian Institute of Science Education and Research (IISER), Pune. It is a part of the activities commemorating "75 years of India's Independence: Azadi ka Amrit Mahotsav" at ARIES.
The 5-day workshop had a theme for each day – Earth, Air, and Spaceflight, Exploration, Space Radiation & Biology, Space Situational Awareness & Opportunities. It included a wide variety of talks in the areas such as cosmic rays, solar monitoring, space exploration, space weather and its effects on satellites and astronauts, astrobiology, balloon-based studies by experts working in the respective areas. Hands-on sessions on application of artificial intelligence and machine learning tools in these areas, which are useful in modern data analyses and modelling techniques, were also organised. The workshop also included a US-India space exploration dialogue session involving eminent scientists from India and the USA.
23-Dec-2021: Scientists trace first clue to understand transient high energy pulses from magnetars several thousand times to that of the Sun
Scientists have found the first clues to understand violent short duration flares from a compact star of rare category called magnetar located thirteen million light years away. These compact stars with the most intense magnetic field known, of which only thirty have been spotted so far in our galaxy, suffer violent eruptions that are still little known due to their unexpected nature and their short duration. Scientists have long been intrigued by such short and intense bursts --- transient X-ray pulses of energies several times that of the Sun and length ranging from a fraction of a few millisecond to a few microseconds.
When massive stars like supergiant stars with a total mass of between 10 and 25 solar masses collapse they might form neutron stars. Among neutron stars, stands out a small group with the most intense magnetic field known: magnetars. These objects, of which only thirty are known so far, suffer violent eruptions that are still little known due to their unexpected nature and short duration, of barely tenths of a second.
A scientific group headed by Prof. Alberto J. Castro-Tirado from the Andalusian Institute of Astrophysics (IAA-CSIC) studied an eruption in detail: managing to measure different oscillations, or pulses during the instants of highest energy, which are a crucial component in understanding giant magnetar flares. Dr. Shashi Bhushan Pandey from Aryabhatta Research Institute of Observational Sciences (ARIES), an Institute of the Department of Science and Technology worked closely with Prof. Alberto Castro Tirado and other group members in this research which has been published in the journal Nature. This is the first extragalactic magnetar studied in details.
"Even in an inactive state, magnetars can be many thousands times more luminous than our Sun. But in the case of the flash we have studied, GRB2001415, which occurred on April 15, 2020 and lasted only around one tenth of a second, the energy that was released is equivalent to the energy that our Sun radiates in one hundred thousand (100,000) years. The observations revealed multiple pulses, with a first pulse appearing only about tens of microseconds, much faster than other extreme astrophysical transients," said Alberto J. Castro-Tirado, IAA-CSIC and lead author.
It is believed that eruptions in magnetars may be due to instabilities in their magnetosphere or to a kind of "earthquakes" (”starquakes”) produced in their crust, a rigid and elastic layer about a kilometer thick. “Regardless of the trigger, in the magnetosphere of the star a type of waves will be created. These waves which are well known in the Sun, are called Alfvén waves and while bouncing back and forth between the points at the base of its lines of magnetic field, they interact with each other dissipating energy”, points out Castro-Tirado.
The oscillations detected in the eruption are consistent with the emission produced by the interaction between Alfvén waves, whose energy is rapidly absorbed by the crust. Thus, in a few milliseconds the magnetic reconnection process ended and, therefore, also the pulses detected in GRB200415, which disappeared 3.5 milliseconds after the main burst. The analysis of the phenomenon has made it possible to estimate that the volume of the flare was similar or even greater than that of the neutron star itself.
The eruption was detected by the Atmosphere-Space Interactions Monitor (ASIM) instrument, on board the International Space Station. The scientific team was able to solve the temporal structure of the event, by analyzing the minute scale of data for over a year. “Though several papers have been published about the event, as ASIM was the only mission that detected the main burst phase in the entire energy range of photons without saturation, it puts the ASIM instrument in a unique position to unveil some of the secrets surrounding magnetars,” said Nikolai Østgaard from University of Bergen Norway, the second author.
“The detection of the oscillations in GRB 200415 has been a challenge due to the brevity of the signal, whose amplitude decays rapidly and is embedded in the background noise. We therefore owe this achievement to sophisticated data analysis techniques that have been applied independently by individual team members. But it is also undoubtedly a technological achievement due to the excellent quality of the data provided by the ASIM instrument on board the International Space Station", points out Javier Pascual, IAA-CSIC researcher who participated in the work.
“Understanding these oscillations can shed light on the structure of these mysterious objects” states Michael Gabler (University of Valencia, Spain).
These flares had been detected in two of the thirty known magnetars in our galaxy, the Milky Way, but also in two others located in other galaxies. GRB2001415 would be the most distant magnetar eruption captured to date, found in the Sculptor group of galaxies (NGC 253) some thirteen million light years away.
“Detections of giant flares from magnetars are extremely rare. This eruption has provided a crucial component in understanding how magnetic stresses are produced in and around a neutron star,” concludes Castro-Tirado. “Continuous monitoring of magnetars in nearby galaxies will help to understand this phenomenon, and will also pave the way to learn more about fast radio bursts, today one of the most enigmatic phenomena in astronomy”, said Dr. Shashi Bhushan Pandey, one of the co-authors of this article.