Magnetic Mercury

Magnetic Mercury...

     Although too feeble, Mercury has a magnetic field. It is less than 1% in strength compared to that of Earth. Terrestrial magnetic field is a consequence of iron-rich core of Earth. Mercurial magnetic field is also a consequence of its iron-rich core. Both the planets have outer core which is in molten condition and inner core which is solidified due to immense pressure on it. But there is a difference in the way in which the magnetic field of the two planets is generated. In the case of Earth, it is geodynamo effect wherein the field is generated through the movement of molten core itself. In the case of Mercury, where its large-size core is expected to contain sulphur in addition to iron, core properties are somewhat different.

Core of Mercury
[Credit: National Science Foundation]

     Laboratory studies carried out by Jie Li and others from the University of Illinois (USA) have shown that iron crystals separate out from molten iron-sulphur mixture if subjected to very high pressure. Mercury is probably having similar conditions at its core. Iron flakes crystallise out in the outer molten iron-sulphur core due to very high pressure on the core. The iron crystals then move through the outer molten core and settle on inner solid core. According to Jie Li, it is this movement of solidified iron throgh the outer molten core that is responsible for imparting the weak magnetic field observed around Mercury. Whether these inferences are realistic or not will be clear only after NASA'a Messenger spacecraft visits Mercury in the year 2011.

Greatest escape

Greatest escape !

     Black hole is known to swallow everything that comes close to it. But there exists a black hole which itself is running away from its surroundings. This evading black hole is discovered by Stefanie Komossa and her colleagues from Max Planck Institute for Extraterrestrial Physics (Germany). When two galaxies collide, the supermassive black holes at their centres merge. But the newly formed black hole cannot continue to remain at its position, but is kicked away from the merging galaxies. That is what it has happened in this case. The 'compound' black hole, that has formed from a merger of two black holes, is moving away from the galaxies with an enormous speed of 2,650 kilometers per second (9,540,000 kilometers per hour). It is over 100 million times massive than our Sun and is ten billion light years away from us.

Escape of a black hole: Artist's concept
[Credit: MPE/HST]

     This 'super kick' is a consequence of theory of General Relativity and astrophysicists have already predicted such an escape earlier. As the black holes merge, intense gravitational waves are generated. Since these waves propagate in one particular direction,  the compound black hole experiences a recoil in opposite direction. This recoil is so strong that gravity of the merging galaxies cannot stop the movement of the black hole. These predictions of General Relativity have been validated by this discovery of escaping black hole.  The discovery is based on ealier spectral studies carried out with Roentgen Satellite (ROSAT), Galaxy Evolution Explorer (GALEX) and Sloan Digital Sky Survey.

Success of  PSLV continues

Success of  PSLV continues …

     On April 28, ISRO’s Polar Satellite Launching Vehicle PSLV-C9 successfully launched ten satellites in a single mission from Satish Dhawan Space Centre, SHAR. The battery of satellite had 2 Indian and 8 foreign satellites in it. Indian satellites consisted of CARTOSAT-2A and IMS-1, both being remote sensing satellites. While CARTOSAT weighs 690 kg., IMS-1 weighs 83 kg. High-resolution data from CARTOSAT-2A will be used for large scale mapping involving urban and rural development applications. Other eight satellites were nanosatellites developed by Canada, Denmark, Germany, Japan and Netherlands. Total weight of these nanosatellites is 50 kg. It is twelfth consecutively successful PSLV flight. India’s first mission to Moon will use the same vehicle for launching Chandrayaan-1 spacecraft.

Launching of PSLV-C9
[Credit: ISRO]

Untimely end?

Untimely end?

     Celestial objects, which are potentially dangerous to earth, consist of asteroids and comets. But now, one of the planets also may have to be listed as a dangerous object. And this planet is none but Mercury. Mercury's orbit is going to be changed drastically in future. Of course, time required for Mercury to start behaving in extremely chaotic manner will not be short but may be in terms of billions of years. However, it will be little before our Sun reaches red giant stage and engulfs our Earth. Therefore, it may not be the Sun but Mercury that will bring our world to an end. Reprieve is that the chances of this untimely (!) end are only  1% to 2%.

     We think that our solar system is very stable. Simulation studies carried out independently by French and American scientists show that it is not so. This instability will not be manifested for at least 40 million years from now. But after this time period, ill-effects on the path of Mercury will be clearly seen. Jupiter's gravity will start slowly elongating the orbit of Mercury. The eccentricity of Mercury will change from existing 0.2 to more than 0.6 in few billion years. Then Mercury will cross Venus's orbit bringing Venus into trouble. And then it may be our Earth's turn! Mercury may collide with Earth and the later will glow at red-hot temperature for a millennium or so. With this, life on Earth will obviously cease to exist!

Shaky Sun

Shaky Sun...

     Whenever severe earthquake occurs, our Mother Planet experiences global 'postquake' vibrations. These postquake vibrations continue for several weeks. Sun also experiences similar global postquake ripples. Large solar flares induce intense sunquakes and these intense sunquakes, in turn, induce postquake vibrations. These are the observations made by Solar and Heliospheric Observatory (SOHO) spacecraft which is keeping a continuous watch on Sun.

Uprising Sunquake (1996)
[Credit: SOHO/ESA/NASA]

     These peculiar vibrations are not new to astronomers and are known as '5-minute oscillations' (because of their oscillation period of 5 minutes). But the correlation between these vibrations and solar flares was not known so far. The correlation is now clearly established. Whenever the number of flares increases, the strength of the vibrations also increases. Mechanism behind this correlation is not yet understood. But the scientists feel that other sun-like stars also must be exhibiting similar vibrations. In future, it may be possible to use similar phenomenon for detecting the flares on these stars.

Coldest Star

Coldest Star...

     Can you imagine a star to have surface temperature lower than that on the surface of Venus?.....Or lower than day-time temperature on the surface of Mercury? Yes! Such a star exists. International team of astronomers has discovered a star with a surface temperature as low as 350°C. It is a brown dwarf...and also coldest brown dwarf known so far! This brown dwarf is located 40 light years away from us and it lies in the constellation Cetus. It was discovered under the auspices of 'Canada-France Brown Dwarfs Survey' programme, using the telescopes in Hawaii and Chile.

[Credit: Canada-France Brown Dwarfs Survey programme]

     Brown dwarfs are those stars which could not evolve properly. These stars do not have sufficient mass for its core to get adequately  compressed. Core temperature in these stars is not high enough for self-sustaining thermonuclear reactions to get triggered. Consequently, surface temperature of the brown dwarf stars is also very low. These stars can be termed as 'cool stars'. This newly discovered cool star is only 15 to 30 times heavier than Jupiter. Stars are spectroscopically tagged as O, B, A, F, G, K, M, L, T in decreasing order of surface temperature. Probably this particular star represents a new class of ultra-cool stars to be recognised as Y-type stars. Spectroscopic studies have revealed presence of ammonia in the atmosphere of the star. It is first time that ammonia is detected in the atmosphere of a brown dwarf. Ammonia is an important ingredient of the atmosphere of Jupiter. Hence, these stars may form a link between brown dwarfs and Jupiter like giant planets.

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