When the Mariner 4 spacecraft flew past Mars, sending back pictures of a dry, cratered desert, a lot of fantasies and wishful thinking about the planet ended. Even though intelligent, canal-building Martians might not exist, there was a widespread belief there was life on the Red Planet.
Our telescopes could see patches of green, and in the Martian spring, the polar caps partially melted, and a wave of darkening moved from the poles towards the equator. This was interpreted as vegetation greening up as meltwater from the poles reached it.
Guide to the Stars, which was published in 1959, says about Mars: "Vegetable life is certainly very abundant, so animal life may well be present also. Whether intelligent beings akin to ourselves exist on Mars we do not know."
In 1962, Patrick Moore, a well-known astronomer, writer and broadcaster, wrote about the dark patches, "It is highly probable they are vegetation of some sort."
We really wanted to believe.
Earth, Mars and the other planets were born around 4.5 billion years ago, along with the Sun, in the collapse of a huge cloud of cosmic gas and dust. Both worlds formed from the same basic set of ingredients. It is reasonable to assume that the two young planets were similar, with atmospheres and water. Therefore, maybe life got started on both worlds. However, today our world is still warm, wet and bursting with life, whereas Mars is now a frigid, almost airless desert. We believe the main difference in the fates of the two worlds is due to their difference in size. Our planet still has a hot, molten core of mainly iron. Circulation of molten iron generates enormous electrical currents, like a huge dynamo. These generate a strong magnetic field which holds the solar wind away from our planet's atmosphere. Mars, being smaller, cooled faster and its core has now solidified. The magnetic field collapsed, which allowed the solar wind to scour away the atmosphere, leading to the Mars we see today. However, this raises some interesting possibilities.
After all our years of fantasizing about Martian invasions, one finally happened. We invaded Mars. We have robot orbiters, landers and rovers exploring the planet, and more are on the way. They are showing us a desert world with dry watercourses, riverbeds, deep canyons, dry lakes and dry oceans.
Billions of years ago there was water and a thick atmosphere. If life formed on our warm, wet planet, why not on that ancient, warm, wet Mars? If so, has any of that life managed to adapt to current Martian conditions? There is ice below the surface of the planet. Moreover that ice melts sometimes and appears briefly on the surface. The temperature on a warm summer's day at the equator can reach 20 C, although it will plummet to far below zero at night. There are creatures here on Earth that can survive such extremes, so why not on Mars. If Martian life is now extinct, are there traces we can search for?
The Perseverance Rover was sent to Mars to search for present or past life. It is exploring a river delta where water flowed into an ancient lake. The idea is to use that ancient river as an "evidence collector." As rivers flow over the landscape they pick up sediments and other materials. As long as they continue to flow quickly, the material continues to be carried, and maybe more is picked up. Then, when the river flows into the sea or a lake, it slows, and drops what it is carrying, forming a delta. This ancient delta on Mars could contain accumulated biological material. The robot has successfully found complex organic (carbon-based) molecules, which suggest the presence of living things at some point. Work is going ahead to check out this result and to seek more evidence. Our fascination with Mars has not gone away and won't for a long time yet.
• Venus and Mars lie close together very low in the west after sunset.
• Saturn rises during the evening and Jupiter around midnight.
• The moon will reach first quarter on the 25th and be full on the 1st.
Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory near Penticton.
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