I wrote the first version of this app nearly 20 years ago in the Java programming language: the preferred choice a long time ago for embedded Web applications. Not anymore; Java has since been banished from modern browsers and as a result, my beautiful "seas of..." applet ceased to function.

Well, that's not the case anymore! Here it is again, in (almost) its former glory, now in proper JavaScript. Without further ado, here's the app for you to play with; explanations follow below.

Planet:    Sea level altitude:  meters.

To use this program, set the sea level altitude to the level of your choosing (meaningful values are between -10000 and 20000 meters), and click the Redraw button. You may also select a different planet.

The Seas of Mars

No doubt you've heard of the intriguing possibility that Mars was one day covered with water. Thanks to altitude information obtained by the Mars Observer Laser Altimeter, it is now possible to see what Mars would look like today, were it covered with an ocean. The applet here does just that: it shows a map of Mars with the sea level set at the altitude you choose.

I think you'll find this map has many practical uses. For instance, if you wish to consider purchasing Martian real estate, you might want to be careful not to buy a lot that'll be covered with water too soon. The highlands may not be a good investment either; what good is a piece of land that'll remain thousands of miles from the nearest body of water throughout most of the duration of any reasonable terraforming project?

This program utilizes data downloaded from the Mars Observer Laser Altimeter Web site. The inspiration came from the Astronomy Picture of the Day Web site.

It may be of interest to Hungarian readers that the original Seas of Mars applet was once featured by Prim Online.

The Seas of the Earth

After I built the original Seas of Mars applet, someone asked an interesting question: why don't I do a Seas of Earth page?

Intriguing idea. We all know what the map of the Earth looks like, but what would it look like if our planet had a lot more, or a lot less, water?

Finding altitude data for our home planet wasn't terribly difficult: It didn't take long to stumble upon the ETOPO2 database, where I found downloadable data sets, which I quickly converted to the format that my applet can accept. So here it is: your very own Earth to experiment with!

The Seas of the Moon

Astronomers of the past have named large, flat areas on the Moon's surface Mare, Latin for Sea. Whether or not they actually believed that these were real seas on our satellite, we now have the means to see what the Moon would look like, were it actually partially covered with water. The interactive map below uses altitude data from NASA's Clementine mission.

The Seas of Venus

Venus is both more difficult and less interesting. More difficult because accurate data is hard to come by. NASA's Magellan mission has used radar to create a topographic map of most of the planet's surface, but this information is considerably less accurate than the Mars Observer Laser Altimeter data. There are also areas not covered by Magellan radar.

Even so, I was eventually able to locate a suitable data set and modify the Java applet below to demonstrate what Venus would look like, were it flooded with an ocean. As it turns out, Venus, once dubbed Earth's "sister planet", is a lot less Earth-like in this respect than Mars! Whereas Mars has a well-defined "coastline" and an ocean (although the true nature of this northern depression remains a subject of debate), the surface of Venus lacks such coastlines and easily identifiable continental landmasses. Venus is also a lot more flat than Mars; set the altitude to -1200 meters, for instance, and you'll notice that all oceans will have completely disappeared. (In contrast, the deepest spot in Earth's oceans is more than 11,000 meters under mean sea level, in the Mariana trench.)

A Venus topographic map is also much less practical than a Martian one. Whereas the problem on Mars is cold and vacuum (both of which can presumably be dealt with by a future, multi-generation terraforming effort), on the surface of Venus the temperature is hot enough to melt lead, and the atmosphere, at 93 times terrestrial pressure, contains some of the most corrosive gases known to man.

The Venus map uses data downloaded from NASA Planetary Data System node at Washington University in St. Louis. Gray represents areas not covered by Magellan radar.