Venus is a lot like the Earth with almost the same diameter (12,100 km versus Earth’s 12,740), it possesses about the same mass (5 versus 6 x 1024 kilos), it orbits the Sun a bit closer in than we do (109 million km versus 147). The total carbon content of the planet is similar to ours, too. It’s also a lot different. While our CO2 is locked up in the oceans and rocks, Venus has all of its CO2 in its atmosphere, which has caused a runaway greenhouse effect. The pressure at the surface is 90 times ours, and the surface temperature is 460° C (almost 900° F). It’s an alien planet.

Until recently it was believed that Venus was also Geologically dead, with little surface changes evident. But according to the team of scientists who took this data, this indicates that Venus was geologically active no more than 2.5 million years ago, and these features may have formed as little as 250,000 years ago and the fact that the hot spots are still around is a strong indicator that activity is still present on Venus.

“Based on a wide range of estimates for rates of volcanism on the surface, we find an upper bound of 250 years to 2.5 million years,” said lead author Suzanne Smrekar from JPL.

Hot spots on Venus

Smrekar also said the temperature variations aren’t huge. “Only a degree or two above the background temperature,” she said. “‘Hot spot’ refers to the geologic environment. On Earth, places like Hawaii where there is hot material coming up from deep inside the Earth to produce volcanism, are referred to as ‘hot spots’.”

One of the reasons Venus is so interesting is that while we study the Earth it often helps to have something else to compare and contrast with. Venus also holds lots of questions for us to try and answer. Why did Venus suffer such a catastrophic runaway greenhouse effect? Why is its surface apparently pretty much all one age (except for this new result)? Why are there hot spots, and are they like ours here on Earth?

“This view looks toward the sunlit side of the rings from about 48 degrees below the ringplane. Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were acquired with the Cassini spacecraft wide-angle camera on Feb. 28, 2009 at a distance of approximately 1 million kilometers (620,000 miles) from Saturn. Image scale is 59 kilometers (37 miles) per pixel.”

Shadow and Ringshine March 16, 2010: Credit: NASA/JPL/Space Science Institute

This view looks toward the southern, unilluminated side of the rings from about 10 degrees below the ringplane.

The image was taken in visible blue light with the Cassini spacecraft wide-angle camera on Jan. 2, 2010. The view was obtained at a distance of approximately 2.3 million kilometers (1.4 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 102 degrees. Image scale is 131 kilometers (81 miles) per pixel.

Cassini art. Credit: NASA/JPL/Space Science Institute

January 2010 is a great time of year to find Mars in the night sky. Each evening it rises about 7.30 and it is easily identified with a very red glow in the sky. The main thing is where to look. Over the next few weeks it gets closer and closer and makes for easy viewing.

Viewing Mars

January and Feburary are the best months to observe Mars for a couple of years as the Earth passes between Mars and the Sun on January 29th(called opposition. Mars will be due south around midnight so highest in the sky. Oppositions of Mars occur at intervals of approximatly 780 days but, because Mars has an eccentirc orbit (as has the Earth to a lesser extent) the distance of Mars at opposition varies widely. If Mars is at its closest point to the Sun (at perihelion) and the Earth at its most distant point from the Sun, the distance between the two will be at its smallest and so Mars will have its greatest angular size. This happened two apparitions ago when Mars was at its closest for ~ 60,000 years and had an angular size of 25 arc seconds. At the opposite extreme when Mars is at aphelion, the angular size only reaches ~14 arc seconds and, sadly, this is the case this year. Closest approach is on 27th Jan at a distance of nearly 100 million kilometres when its magnitude will be -1.3. Very nicely, it then lies in the constellation of Cancer just above the Beehive Cluster. The Moon, near full will be in attendance to as shown in the chart which shows its motion westwards across the sky over the next few weeks. The fact that its angular size is not as big as it can sometimes be is partly compensated for by the fact that it reaches an elevation of around 60 degrees, so the atmosphere will not impede our view as much as when it is lower in elevation.

Why Earth and Mars are so close

To see significant detail on the surface requires a telescope of 4 inches or more. As the north pole is tilted towards us, we should be able to easily spot the, brilliant white, north polar cap. A slight pity for those with small telescopes is that the most prominent dark feature, Syrtis Major, passes behind the limb in the early evening, so will not be best seen. As Mars’s day is similar in length to ours, we will see a similar face at a given time over quite a long period. The free Planetarium program “Stellarium” will show you what could be seen at any given time of the night during the apparition.

Jan 1, 2010

Mars shines at mag -0.77 in constellation Leo with an apparent diameter of 12.67″. Distance from Earth is 0.73885 AU (111 million km).

Jan 9, 2010

Mars leaves constellation Leo and enters Cancer again, during retrograde opposition loop.

Jan 11, 2010

Apparent brightness of Mars exceeds -1.0 mag.

Jan 27, 2010

Closest approach of Mars and Earth (0.664 AU = 99.33 million km). Apparent diameter of Mars is 14.105″.

Jan 29, 2010

Mars opposition on Earth, Earth in inferior conjunction on Mars. Apparent brightness of Mars reaches -1.28 mag in constellation Cancer.

Elliptical Orbit

That change in distance is about 5 million kilometers, and is a small fraction of our distance from the Sun, so it doesn’t change the Earth’s temperature very much: a few degrees Celsius, but that’s about it. This is NOT the cause of our seasons….

The only reason I mention this is that is FREEZING here in Dublin, and it feels sort of ironic that we are as close as we get to the Sun. Yes I know about tilt and how it causes seasons….Its just cold right now! So I am off for a hot whiskey. Let me know if the sun appears a bit bigger, just don’t use a your new telescope to check Oh, and give  a thought to just how hot the Sun is. It is heating up a planet 93Million miles away….

Our Sun...

Titan Casts a fuzzy shadow.

Titan’s orbit is almost exactly in the same plane as the rings, and having its shadow  so far south of the rings’ shadow is an indication that the Sun is shining down on the planet from just north of the equator. Because the rings are closer to the planet you can just barely see that the shadow they cast is just south of the equator. Titan’s orbit around Saturn is about 1.2 million km from the planet, about 10 times farther out than the main rings.

The images alone have been worth sending this Mission!

For more information about the Cassini Equinox Mission visit http://ciclops.org, http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.

Credit: NASA/JPL/Space Science Institute

Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA). Acknowledgment: M. Wong (STScI/UC Berkeley) and C. Go (Philippines)

“This picture was taken with Hubble’s Wide Field Planetary Camera 2 on 24 February 2009, when Saturn was at a distance of roughly 1.25 billion kilometres from Earth. Hubble can see details as small as 300 kilometres across on Saturn. This close-up view of Saturn’s disc captures the transit of several moons across the face of the gas giant planet. The giant orange moon Titan — larger than the planet Mercury — can be seen at upper right. The white icy moons that are much closer to Saturn, hence much closer to the ring plane in this view, are, from left to right: Enceladus, Dione, and Mimas. The dark band running across the face of the planet slightly above the rings is the shadow of the rings cast on the planet.”

Cassini and IBEX have joined forces to provide additional data which refines our understanding of the Heliosphere. Data from the Cassini Magnetospheric Imaging Instrument (MIMI) and the Interstellar Boundary Explorer (IBEX) shows that the shape of the heliosphere more closely resembles a bubble. Here are two images to help illustrate the difference.

Here is our new understanding of the boundaries.

The Bowshock as we currently understand it

What we until just recently believe is shown below. You can see a tremendous change in our understanding of the shape of the Heliosphere.

Previous understanding of the Heliosphere

The Russians got there first in 1971 when the Mars 3 lander successfully achieved the first official touchdown. It made a 20 second transmission before going silent. The first image from the surface was disappointing, but it did take a wonderful image (shown below) from orbit.

Mars 3 image of Mars

Given the surprisingly large number of missions it is hard to keep track of them. Below is a wonderful zoom-able image showing all of the missions, including those that performed flybys.

Missions to Mars