Category Archives: planets

astronomy, binoculars, planets, stargazing

Getting up Early?

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Check Out Some Planet Action!

Every day is Astronomy Day, although we officially celebrated it  last weekend. But, any day you can check out the Sun (or the Moon, if it’s up), or any night that you can step out and observe something cool in the sky makes it Astronomy Day.

These four bright planets cluster closely together in predawn skies during May 2011. Courtesy Sky & Telescope.com

We’ve been plagued with snow the past two days (although, as we say here in the West: “We need the moisture”), so haven’t been able to do much observing.  Today, there’s a big bright thing in the sky and it’s making water out of snow as I write this.  So, tonight should be a fairly clear night for some good viewing.

If you have occasion to get up early in the morning and you have a good view to the eastern horizon, you WILL be treated to a nice view of four planets, especially if you bring along your binoculars or happen to have a small backyard-type telescope handy. Hey — there’s got to be some reward for getting up before the crack of dawn, right?

Here’s what’s up:  Venus and Jupiter are visible in the pre-dawn sky, together with — if you can spot it (and here’s where the binos or scope come in handy) — Mercury. Together they make a little triangle in the eastern sky.  Venus and Mercury stay within 1.5 degrees of each other for another week, while Jupiter climbs higher into the predawn sky. By mid-May, you’ll be able to spot Jupiter before Venus despite the fact that it’sless than one-quarter as bright.

A week later, Venus and Mercury create a second planetary triangle with Mars, which is quite faint (just 1/100 as bright as Venus). The triad is tightest, just over 2 degrees wide, on May 21st. Venus and Mars close to within 1 degree of each another on the 23rd, by which time Mercury has begun a slide toward lower left.

To top off the solar system action, look for a thin crescent Moon nearby on May 29-31.

The friendly folks at Sky & Telescope.com have a cool animation of these sky events, so check it out!

While you’re out that early (around 4:30 a.m.), also take some time to check out some gorgeous stellar sights.  First off, the summer triangle is visible — look for bright Vega high in the sky. That also means the Milky Way is arcing across the field of view Arcturus is setting the west, and the Big Dipper is low in the northeast — for all you Northern Hemisphere viewers. If you’re in the southern hemisphere, the constellation Sagittarius should be high overhead and the Milky Way should look gorgeous!  If you need a star chart, go here or here to download Stellarium, a free star chart program.

planetary history, planetary climates, planetary science, planets, venus, Venus Express

Planetary Habitability

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What Does it Mean?

In my last blog entry, I talked about oceans on ancient Mars and the evidence for them that planetary scientists are finding in craters on the Red Planet. All the questions about water on Mars really point to a big question about habitability — that is, a world’s capability of sustaining life.  There’s a sort of rote list of things that planetary scientists recite when it comes to assessing what a world has to support living beings. It has to have water, warmth, and organic material (food, essentially) for the life to exist. Those things are important for habitability.  So, if Mars had water in the distant past, and if it had warmth (from volcanism or heating from its core or if it had an atmosphere that could trap heat), then two of the three conditions for life would have been met. Food — organic material — would be a simple chemical problem to solve. Here on Earth, food for life ranges from the stuff you and I eat every day to the needs of such one-celled beings as bacteria that munch on sulfur.  Obviously, early Mars didn’t have gourmet delights that we could eat, but it could well have had plenty of delicacies for one-celled organisms.  So, the planet could have been habitable.  If we decided to live there in the future, it could still be termed habitable, but only just barely and we’d have to bring along habitats to take advantage of the barely habitable landscape. But, it could be done. And, it likely will be done.

So, we know Earth is habitable (still). And, Mars was and could be. But, what about Venus?  You know, that beautifully bright starlike object that’s making a nightly curtain call in our western skies after sunset?  Yeah, that one.  It’s gorgeous to look at, but if you landed on Venus, you’d fry in an instant, if you weren’t crushed to death first by the hellishly heavy and hot atmosphere.  So, how could this volcanic, sulfurous world be habitable?  Clearly it isn’t right now, but it may have been in the past.

What early Venus could have looked like. Could it have had a water ocean? Or was it more likely a molten world with a wet atmosphere? What happened to it? Credit: J. Whatmore.

Scientists at the European Space Agency are operators for the Venus Express orbiter, which has sent back data suggesting very strongly that early Venus could have water — perhaps even an ocean of it — and may have begun its planetary life as a much more Earthlike world. The spacecraft measured the escape of molecules of hydrogen and oxygen from Venus out to space.  The rate of escape of hydrogen is roughly twice that of oxygen, and this indicates that water is the source of these escaping materials. There’s also a tracer element called deuterium that also tells scientists that water has been escaping the planet. Deuterium is a heavy form of hydrogen, and it would have more difficulty escaping the planet’s gravitational pull. The presence of large amounts of it in the upper atmosphere of Venus tells us that water has also escaped and left the deuterium behind.

It’s probably unlikely that Venus had Earthlike oceans as shown in the artist’s concept above.  If it did have standing water, those pools and/or small oceans could have been formed when comets slammed into the molten surface.  If that happened, and if conditions were right, Venus could have been habitable for a short time in its early history. If that’s true, then it begs the question of whether life could have arisen on the planet, only to be snuffed out by Venus’s subsequent changing climate.  It’s an interesting idea and one that needs to be explored more.

However, the more likely scenario is that the newborn Venus had no oceans, but sported a very wet atmosphere overlying the molten surface.  Over time, sunlight broke the water molecules into hydrogen and oxygen (a process known as “photodissociation”). The newly freed gases fled to space, leaving behind the deuterium. The escape process cooled things down enough, and the surface cooled.

There’s still a lot of “ifs” in these scenarios, but the evidence for water (past and present) is strong, based on the Venus Express data.  It’s a good hint that the Venus we see today — hot, arid, miserable, and volcanic — wasn’t always this way.  And, it adds more to our store of knowledge about just when a planet can be habitable in its history — provided the conditions are right.

Stay tuned!