This appeared in Deccan Herald (Spectrum) of May 24, 2016
The space Vehicle DAWN orbiting the dwarf planet CERES
from very near the surface has been giving fantastic
pictures and has also confirmed the presence of water.
The
gap between the orbits of Mars and Jupiter in the Copernican model
of the solar system was large enough to get the attention of many
great scholars including Johannes Kepler, Issac Newton , Emmanuel
Kant etc. The Italian astronomer Giuseppe Piazza working in
Palermo, Sicily discovered a small planet in that gap in 1801.
This coincidentally was in the exact position predicted by
astronomers Titus and Bode. Piazza named the object CERES after the
patron goddess of Sicily ,also in charge of agriculture. Later
many objects were discovered moving in that orbit, the most
important of them being Vesta, smaller than Ceres. These objects,
called Asteroids, are thought to be due to a planet which existed at
the beginnings of the solar system but broke up completely due to
the gravitational tug from the nearby giant planet Jupiter. There
are roughly 1.5 million of these objects with diameter larger than 1
km and only 5 % of them have names. Most of the craters on many
planets and satellites in the solar system are attributed to the
hits of these asteroids. Many meteors from Vesta have been found on
earth which is supposed to be due to huge impacts on Vesta itself
.Ceres and Vesta have surface areas sightly less than that of India
and Pakistan respectively. Ceres has about 7 % of mass of Pluto and
Vesta's mas is about 1/3 of Ceres. While Ceres cannot be seen
through naked eyes the very reflective surface of Vesta makes it
visible without a telescope. Ceres and Vesta are at Twice /thrice
distance of Mars from earth.. Ceres is the only asteroid that has a
shape rounded by the force of its own gravity. Therefore Ceres was
also included as dwarf planet along with Pluto and Eris in 2006.
A
study of these asteroids will tell us how our earth was in the dawn
of the solar system. The planets of the solar system took long time
to get their present shape; for example, Earth and Mars went on
accruing mass for 50 and 30 million years respectively. However
asteroids acquired their present shape quite soon : Ceres and Vesta
in 10 and 7 million years. They could not acquire more mass because
of the overwhelming presence of Jupiter. With this aim, there have
been many specific observations of asteroids in the last few decades.
As for Ceres, there were observations by the Hubble Telescope in
2004 and by the Herschel IR telescope in 2014.
An aptly termed space vehicle called DAWN departed earth in
2007 for the exploration of Ceres and Vesta. This vehicle was the
first ever to (a) orbit two celestial bodies beyond Earth (b)
orbit an object in the main asteroid belt. With a speed of 40000 km
per hour it passed Mars in 2009 and reached Vesta in July 2011. It
surveyed the asteroid from about 200 km from the surface for several
months. It left Vesta in September 2012 and took about 3 years to
reach Ceres. After traveling nearly 5 billion kms, it started
orbiting Ceres from March 2015 . In Dec 2015 it started surveying the
planet from a height of 385 km and has provided magnificent views
of the celestial body. While the mission could end in 2016, DAWN
will remain in orbit for ever around CERES though it wont be sending
any signals. In its lowest-altitude mapping orbit, at a distance of
385 kilometers from Ceres, DAWN is nearer to the planet surface
than International Space Station is to earth!
RECENT
RESULTS FROM DAWN
An
important feature of of Ceres from the earlier days has been the
presence of large bright spots suggesting watery ice on the surface.
DAWN has been able to take a very close look at these bright spots
from a very near distance. Th two big ones are the the Occator
and the Haulani craters with breadths of 100 km and 34 km . One has
a dome like structure in the pit and the other a central ridge.
The intricate geometry of the craters , the color of the ejected
material etc suggest geologic activities and impacts in the recent
past. The spots could be due to briny water erupting from the
interior and later sublimating leaving behind the salt deposits
.There is also the possibility that the interior is supplying fresh
salts (containing Magnesium, Ammonia etc) to the region. The shape
of the craters is exceptional in being polygons since most craters
elsewhere are circular !
There are also further evidences to believe that Ceres has
large amount of ice and may even have subsurface liquid water. Few
years ago, Herschel IR Telescope showed water vapor coming from
two dark patches of ground with the estimate that the loss was
about about 6 Kg of water per second. This proves that Ceres has a
icy surface and also an atmosphere. DAWN has shown in the past few
months that the 10-kilometer-wide OXO Crater , the second-brightest
feature on Ceres, harbours water either in the form of ice or
hydrated minerals .
It is possible that Ceres has more water than all the fresh
water on Earth; however Ceres' water, unlike Earth's, would be in
the form of water ice and located deep in the mantle. While the
presence of water has been noted in several comets, finding of water
on Ceres shows that impact of asteroids also must have brought water
to earth. For this reason, the idea of colonizing Ceres someday has
some appeal, compared to distant objects like Europa and Titan.
Pic 1 -
Haulani crater with the shape of a polygon shows results of fresh
impact
Pic 2 -
Center of Occator crater with many details
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