Cloudspotting on Mars

The Observations

How does the Mars Climate Sounder (MCS) detect clouds?

Unlike cameras that look at visible wavelengths of light to take pictures of Mars (which can see clouds), Mars Climate Sounder measures infrared light. From its position in orbit above Mars, it looks at the horizon of the planet, "seeing" heat from near the surface to higher altitudes. Because clouds emit in the infrared, they stand out with respect to the empty sky. They look like arches because the spacecraft (MRO) is moving around the planet, so the "apparent" altitude of the cloud changes.

Of course MCS doesn't just look for clouds -- it measures vertical profiles (from near the surface to 80 km every 5 km) of temperature, pressure, dust, and ice. These help us understand the weather and climate, including dust storms -- a defining feature of Mars's atmosphere.

When did MCS begin measuring the atmosphere?
In 2006 -- it's been at Mars for over 16 years! Such a long baseline presents an opportunity to study how clouds change with season and from year-to-year.

What is a Mars Year (MY)?
A Mars year takes 687 Earth days. Mars Year 0 (MY0) is defined to start on May 24, 1953. Instead of named months of the year we use on Earth, we track solar longitude, "Ls" (pronounced "ell sub ess"), which corresponds to Mars's position in its orbit around the Sun. Here is a tool to convert MY and Ls to an Earth date, and from Earth date to Mars MY and Ls. Check out this article to learn more.

You can find the MY and Ls of each image you classify by clicking the "i" metadata button below the image on the bottom right.

What are the axes in each image?
The horizontal axis is time. Each file spans 4 hours from left to right. In that time, the MRO spacecraft completes a little over 2 full orbits. The vertical axis is altitude from 0 to 110 kilometers.

Where can I find the raw data?

The data used for to create the images for this project -- time-altitude plots of infrared measurements by MCS -- are available at the Planetary Data System. In the metadata for each image, you'll see a link to the L1b ("level one-b") data (the raw data files used to create the image) and to the L2 ("level two") file (containing derived data products from the measurements: for example, temperature, water-ice opacity, and dust opacity) covering the same period as in the image. Learn more about the MCS observations and data files here. To work with the raw files, see repositories in the project Github.

The Science

How do clouds form on Mars?

Both water-ice and carbon-dioxide-ice clouds form on Mars. While we think of Mars as a cold and dry planet, the atmosphere does contain some water vapor. If a parcel of Martian air with water vapor becomes cold enough, water vapor can condense into an ice crystal. The cold temperatures and low pressures in the atmosphere lead water vapor to transition straight to ice instead of liquid droplets. It is uncommon for clouds to form from the main constituent of the atmosphere of a planet. But in some locations on Mars, especially at high altitudes, temperatures can drop low enough such that carbon-dioxide ice crystals form (most of Mars's atmosphere (95%) is CO2). Another ingredient is important for cloud formation: cloud condensation nuclei. These are particles in the atmosphere on which water or CO2 is able to condense on. These can be dust particles or, for CO2 clouds, water-ice particles, or maybe even "meteoric smoke particles" that come from meteors that enter the atmosphere from space. Differences in the compositions and particles of the clouds lead to differences in how they warm or cool the atmosphere.

Do high altitude clouds form on Earth?

They do! Noctilucent clouds form around 50 miles up in Earth's atmosphere. These thin icy clouds, because they are so high, reflect light after the sun has set---"noctilucent" means "night shining." Learn more!

Do we have pictures of Martian clouds?

Clouds form every day on Mars and we have lots of pictures from our orbiters! Here's an example:

[Credit: NASA/JPL-Caltech/Malin Space Science Systems]

And be sure to take a look at clouds seen by the Mars rovers drifting across the sky!

Identifying Clouds

I can't quite tell, is what I see is an arch?

We suggest only labeling an arch if you see two bright sides with a bright peak at the top and if the arch is noticeably brighter than the background. There is a lot of variability in brightness in each subject and changes with altitude; only label features that stick out as arches (but be sure to flip through the multiple images which attempt to stretch the contrast!). Check out the Field Guide for many examples that might help. We also recommend discussing images you have questions about with others in the Talk board.

I made a mistake, how can I fix it? How can I redo an image?
Don't sweat it! Many people will look for arches in each image, so it's ok if you think you made a mistake in a previous image. Unfortunately, there is no "redo" button, so once you click Done, your markers are set. Put it behind you and move on! But maybe take an extra minute to click back through each frame and double check your markers on the next one.

Getting involved

How do I join the Cloudspotting on Mars Community?

If you'd like to get involved at a deeper level, we invite you to join our community. Just reach out to us at cloudspottingonmars@gmail.com and ask to join the community. Looking forward to hearing from you!

You can also check out our Github page and our blog for more information and opportunities to do more.