Looking for Planet B

By wildgirl -

Home for human beings is planet Earth: we were formed by conditions here even as we are now affecting the climate. Scientific explorations aside, Dr Anjani Ganase asks us to appreciate why there may be no other planet so perfectly suited to human life.

Recently scientists discovered a planet outside our solar system that rained iron owing to extremely hot temperatures that soared to 2400 degrees Celsius. Yet, even within our own solar system, the other planets have extreme weather patterns and atmospheric conditions that are very different from our planet. Considering the environment of Earth -   20 % oxygen and 78 % nitrogen, 24 hour day cycles, mild temperature ranges and a protective atmosphere - will quickly highlight how much we are adapted to our unique environment as well as help us to understand how rare our unique environment is. The resources needed to adapt and the feasibility of living elsewhere at least as comfortably as we live on Earth should persuade us  to invest instead in conserving our home. Let us look at the other planets in our solar system.


Pluto
Pluto is the farthest planet in our solar system; it is a dwarf just over three billion kilometres away from the sun. Because of this distance, Pluto only receives 1/900 the light that comes to Earth. Pluto is known as a frozen planet with mountains of ice and frozen gases. As it is so cold, Pluto is unlikely to be able to support any life, since water in the liquid form is a necessary medium for life. The temperature of Pluto can get down -220 degrees Celsius. Pluto takes an extremely long time to orbit the sun, approximately 243 years, while its rotation is also very slow where a single day on Pluto lasts 153 hours or just over six earth days. As Pluto orbits the sun, it does so in an elliptical manner. Therefore, there are times when Pluto may be closer to the sun than other planets in the solar system. The atmosphere of Pluto is extremely thin and is absent of oxygen, as well as having one sixth the gravity of earth owing to its small size.

Composite of Jupiter and the many swirling storms that occur. Image data: NASA/JPL-Caltech/SwRI/MSSS Image processing by Kevin M. Gill, © CC BY

Jupiter
Jupiter is known as the gas giant in our solar system because Jupiter actually has no solid surfaces to land. There may be a solid core, but this is still a mystery to many scientists. The atmospheric pressure close to the centre of the planet is likely to be 40 million times the sea-level pressure on earth. Such pressures allow for a large ocean of liquid hydrogen to form under these unimaginably extreme conditions. Jupiter is also famous for having a visible Great Red Spot that’s larger than the size of Earth. This is a giant storm that has been swirling for hundreds of years with winds up to 400 mph. This may be the result of Jupiter’s rapid spinning with only a 10-hour day. Jupiter also has many moons and while the environment of Jupiter may be extremely harsh, conditions on some of the larger moons are regarded as mild by comparison. On Europa, one of Jupiter’s moons, scientists have discovered a vast ocean under ice which potentially may be able to harbour life.

Let’s have a look at Earth’s two immediate neighbours, Venus and Mars. While closest in proximity they are still quite distinct from Earth’s ideal conditions. Earth seems to have been formed in the “sweet spot” with regard to the distance from the sun, in order to support life as we know it. This means that our temperature range supports the formation of liquid water, the source of life; planets too far from the sun are frozen with ice and too close water is vaporized.

Venus composite. Photo Credit NASA/ JPL-Caltech





Venus 

Venus is our near neighbour closer to the sun, making it hotter than Earth. With regard to structure and size, Venus is similar to Earth as it has an iron core and a rocky crust that forms great mountains and valleys. While Venus isn’t the closest to the sun, it is the hottest planet in our solar system. This is because of Venus’s dense atmospheric conditions, described as having a runaway greenhouse effect. It is mostly composed of carbon dioxide with sulfuric acid clouds, and temperatures soar to 470 degrees Celsius.  Any attempt to send spacecraft to Venus failed because of the intense heat stress on the electronics systems. Such hot conditions make Venus seem implausible for supporting life. However, scientists speculate that life may have occurred there in the past.
 
Mars image composite of the Valles Marineris: The Grand Canyon of Mars captured by Viking Orbiter 1. Photo Source: NASA/JPL-Caltech 

Mars 
Mars is the most explored planet apart from our own. Mars is about 223 million kilometres from the sun a mere 131 million kilometres farther from the sun compared to earth. Mars is a cold desert planet with no visible sources of water. It’s been compared to some of the harshest places on earth, such as the Atacama Desert in Chile, the dry valleys in Antarctica and Death Valley in California. The Martian atmosphere is 96 % carbon dioxide. One similarity with Earth is the length of the day, which is about 24.6 hours. However, Mars revolves around the sun more slowly and has 687 days in its year. Mars is known as the red planet because of the oxidised iron found on its surface which creates a very dusty surface and lots of dust storms. Although the temperature on Mars can get up to a pleasant 20 degrees Celsius, it can also drop to -153 C. The thin atmosphere means it can trap very little heat. While Mars has been heavily investigated for its possibility to support human life, the sustainability of this is a long way away.

Earth
Our planet Earth with its Ocean has shaped us: we believe Earth belongs to homo sapiens. Perhaps we need to change our perspective to see how we are distinctive creatures of our unique planet: we belong to Earth. The one thing space exploration has taught scientists is the irreplaceable value of our blue marble, our watery home. Sometimes we need to look upwards and outwards to appreciate what we have near at hand.

References:
https://solarsystem.nasa.gov/planets/overview/

Ehrenreich, D., Lovis, C., Allart, R. et al. Nightside condensation of iron in an ultrahot giant exoplanet. Nature, 2020; DOI: 10.1038/s41586-020-2107-1
                                       


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