After twenty years - End of Mission for Cassini

After 13 years in orbit around Saturn and 20 years in space, the Cassini Mission has come to an end. Launched on 15 October 1997 as a cooperative project between NASA, the European Space Agency (ESA) and the Italian Space Agency, the four year prime mission carried the Huygens probe to Saturn with its tour being extended twice. Amongst many discoveries two key ones were on Saturn's Moons, the global ocean and indication of hydrothermal activity within Enceladus, and liquid methane seas on Titan.

As Cassini's rocket fuel used for adjusting its course was almost exhausted rendering control of the course of  the space craft impossible, the decision was taken by NASA to dispose of the orbiter in Saturn's atmosphere. This ensures that Cassini cannot collide nor contaminate Saturn's moons and affect any future studies of habitability and potential life on those moons. The orbiter will plunge into Saturn's atmosphere on September 15, 2017.

Link to the Cassini website:
Cassini website - NASA 

Dawn at Saturn - from 1.23 million kilometres away (c) NASA JPL

Mission to Mars - an unreachable goal for the forseeable future

Mars composite image - (c) Jet Propulsion Laboratory

Mars, the planet which has conjured many a science fiction movie and not a few novels. Seemingly close, the nearest planetary neighbour to Earth is nonetheless very distant to this planet and travel over such a large distance poses both technical challenges and extreme health risks for humans attempting the voyage.

In terms of orbit around the Sun, Mars is always 48.3 million or more kilometres away from the Earth which equates to around 140 times further than the moon. In terms of transit time, this distance would mean around 210 days to travel from the Earth to Mars depending on the best available launch window and capability in velocity based on the existing propulsion systems or those in the design stages. Once at Mars, a mission team would need to wait around 496 or so days before being able to commence a return flight to Earth.

What sort of space vehicle would be able to both propel the pay load safely to Mars and be able to sustain a flight crew during transit to the planet ? It would need to have sufficient speed to cover the distance with a size and scale to include the necessary life support functions including air and water to sustain the crew. Existing fuel burning engines would not suffice due to the amount of fuel which would need to be carried and a solar powered vehicle would be slow moving indeed. Mounting a nuclear engine on a manned space vehicle carries its own multi-level high risks.

The technology to reach Mars is not insurmountable however the physical health ramifications for astronauts may yet pose an almost impassable barrier. Existing data from Moon missions, Skylab and the International Space Station have demonstrated the punishing effect of long term exposure to weightlessness  on the human body - bones waste away at a rate of one percent of bone mass per month; fluid can collect behind eyeballs and cause blurred vision; radiation from solar flares and cosmic rays (which are high energy particles travelling at close to light speed) pose a direct threat to DNA and human brain cells. These are only the known factors as already identified with potentially many more.

So Mars travel remains a dream at the moment. NASA and private companies such as SpaceX have the intention to reach the red planet but for the now the only visitors will remain remote mobile robotic devices scanning the landscape for, as yet, undetected discoveries.

Strata at the base of Mount Sharp, Mars: (c) NASA Mars curiosity rover

                                                     

The fragility of life - are the aliens dead ?

Figure 1: Scenarios A) B) and C)

Despite the realisation that there are literally billions of stars, exoplanets, planets and other celestial bodies in the Universe, the perplexing reality is that proof of life on other planets has been impossible to obtain despite decades of effort. Programs such as SETI and observational work through telescopes (Hubble, Spitzer, Kepler and in the future TESS and James Webb) has done little to establish the existence of life on another planet. 

Chopra and Lineweaver, in a controversial paper, have proposed a Gaian bottleneck theory to explain the low or non-existence of life while making the telling observation that archaeological excavations have not unearthed alien spaceships and optical and radio searches for extraterresttrial intelligence have not been successful.

The Gaia hypothesis, (theory or principle), contends that organisms interact with their inorganic surroundings on Earth to form a self-regulating complex system that plays a critical role in maintaining the conditions for life on the planet. Within this paradigm are key components such as the way in which the biosphere and the evolution of life forms affect the stability of global climate, ocean salinity, oxygen in the atmosphere and other environmental variables that affect the habitability of the planet.

According to Chopra and Lineweaver, a Gaian bottleneck exists whereby if life emerges on a planet, it only rarely evolves quickly enough to provide activities which regulate greenhouse gases and albedo, thereby maintaining surface temperatures compatible with liquid water and habitability. This bottleneck theory therefore suggests that first, extinction is the cosmic default for most life on the surfaces of wet rocky planets and second, rocky planets need to be inhabited to remain habitable. Almost a Catch 22 situation.

The emergence of life's ability to modify its environment and regulate initially abiotic feedback mechanisms is termed 'Gaian regulation'. As far as Chopra and Linewear are concerned, without rapid  evolution of Gaian regulation, early extinction would be the most common outcome for planetary life. As continuing efforts are made to search the universe to locate and identify life, the Gaian bottleneck model suggests 'that the vast majority of fossils in the Universe will be from extinct microbial life.'

Three scenarious are shown in Fig 1 above - A) Emergence bottleneck, life rarely emerges even on rocky wet planets; B) No bottleneck, life emerges with high probability and lasts for billions of years; C) Gaian bottleneck, life emerges but goes extinct within a billion years.

So, the chances of finding any form of life, under this model is close to zero and what evidence may be found will have long been dead. 

Chopra and Lineweaver's paper can be accessed here:

The Case for a Gaian Bottleneck: The Biology of Habitability

Gas and dust form planetary disks - formation - image courtesy NASA

Up in the Sky - NASA releases images from Wide Field Infrared Survey Explorer

NASA's Images from looking into the heavens: click here

Nebula SH 2-235

Searching for ET - a flawed perspective

Within some astronomy circles there is a view that searching for extraterrestrial life in the universe is a good and worthy goal, both from a scientific point of view and the resources needed to carry out such research. Hollywood films such as 'ET', 'Close Encounters of the Third Kind' and 'The Day the Earth Stood Still' paint a picture of higher intelligence being understanding and interaction with people on this planet being one of positivism or curiousity. But on what basis would an assumption along these lines bear any resemblance to reality? The recent release of a muddled mess of a film called 'Skyline' presents a different view of aliens. In this film they are portrayed as overtly hostile and their arrival on earth is aggressive with humans seen as resources to be harvested. In 'Skyline', the human race is not successful  at beating off the invaders and succumbs to the more powerful alien force. It should not presumed that any life form outside of this planet would subscribe to the same values, beliefs or behaviour often recognisable to homo sapiens. The Universe in fact is a highly hostile and volatile environment and should any intelligence be found which has the capacity to reach this planet, it is unlikely to have benign behaviour or adherence to ethical and moral values.

Life beyond in the stars?

The recent pronuncement that Gliese 581g, a planet orbiting the red dwarf star Gliese 581 may be suitable for life should not come as any surprise. Located approximately 20.5 light years away from Earth in the constellation of Libra, the planet is located in the middle of the "Goldilocks" zone, or what is defined as a habitable part of space near its parent star. The existence of liquid water is considered a strong possibility and this condition is generally considered a precursor for life. The planet was discovered by the Lick-Carnegie Exoplanet Survey following a period of over ten years of observations. Gliese 581g is believed to be the first Goldilocks planet ever found being the most earth-like planet with the potential for harboring life. The search for life in the universe continues both through optical astronomy and radio astronomy (the SETI program). The question remains, if life is found, what would the human race do?