From the Inner Solar System...

This post is the second update on the current state of exploration in our solar system. This installment will skip Mars, although there is still plenty to talk about. I'll refer you back to my previous posting and mention that the dust storm circling the planet is still delaying the entry into Victoria Crater. Stay tuned!

Quick! What's the second-most under-visited planet in our solar system? It's easy to answer what planet (sorry IAU) is the most neglected, that being Pluto. The second most neglected body in our solar system is Mercury, the innermost planet. Visited once previously in a series of flybys using the Mariner 10 probe, only about 50 percent of its surface has been photographed in any detail. Seeing that was in 1975, a return visit is more than overdue!

The current mission is known as Mercury MESSENGER (MEcury Surface, Space ENvironment, GEochemistry, and Ranging, get it?). Launched in 2004, the probe will finally arrive in mercurian (hermian?) orbit in 2011, after a journey that involves one flyby of Earth, two of Venus and three of Mercury itself before finally settling into orbit. Unlike some missions where a flyby might be used to boost the spacecraft's speed (such as the recent encounter between the Pluto-bound New Horizons probe and Jupiter), these multiple flybys are being used to change the speed, size and tilt of the Mercury MESSENGER's path to enable it to use its relatively small engines to settle into orbit around Mercury.

What then? We have lots of questions, hopefully we'll get more than a few answers. For example, of the four "rocky" planets, Mercury is the smallest of the batch, has densest makeup, the oldest surface and the most extreme temperature variations. MESSENGER will probe the surface with a variety of instruments to try and determine the makeup (and therefore, which theory of evolution was the most likely). Imaging the surface will build a more detailed maps. Does Mercury have a liquid core (it shows a magnetic field)? Is there ice (water ice?) at the poles?

Mercury has been an enigmatic planet both in history and science fiction. Think of what you've read that has been proven wrong. A twilight belt. A half-molten/half-frozen surface. A place of weird creatures. You know something? What we really find there might be even more exciting and strange!

Mercury MESSENGER's mission is expected to last for one year. After that, we might see the joint Japanese-European twin probe known as BepiColombo, which is planned to orbit the innermost planet for three-and-a-half years.

So what about our "twin", the cloud-shrouded planet Venus? Not quite as neglected as Mercury, there also has been a long gap in explorations there. Currently, there is one visitor from Earth in orbit, the ESA's Venus Express. Built mostly from spares from the Mars Express and Rosetta missions, Venus Express was designed to orbit Venus for two days (Venusian days, that is...about 500 Earth days!) and pierce some of the clouds of mystery.

Does Venus have a liquid core? Are there active volcanoes on the planet (the surface appears to have been shaped by volcanic activity in the past, is it still undergoing eruptions?)? Why are craters on the surface distributed fairly uniformly? Does this mean that the surface has been massively reworked? What is the link between the geology of Venus and the climate? What are the atmospheric mechanisms for things such as the rotation of the atmosphere (many times faster than the rotation of the planet)?

Being so close, yet so different, from Earth makes Venus an interesting object to study. There is a lot of concern here on Earth that we are heading into a period of global warming. Venus is an extreme case of global warming; might it be useful as a model to study that?

Want to see Venus yourself? Look in the western sky, after sunset. It's currently one of our "evening stars" and (next to Jupiter) the brightest object that you can see.

As an addendum, even old missions can yield new results. For example, take a look at these images from the Soviet Venera landers. The data was reprocessed and cleaned up, yielding stunning images of one of the most hostile places in our solar system.