Midnight Planets keeps up-to-date with the latest images from the Mars rovers Curiosity and Opportunity; both the app and the website are automatically updated with the latest available data. Here’s how it works:
Almost every day, the engineers at NASA/JPL send commands to the rovers on Mars. At some point during the Martian day, which is called a sol, the rovers take pictures and send them back to Earth. Usually the rovers communicate with Earth by way of two satellites in Mars orbit, Mars Odyssey and Mars Reconnaissance Orbiter, which pass over the rovers at certain times during the day. The satellites send the images to Earth, where they are received by the Deep Space Network of antennas. From there they go to NASA/JPL, who processes the images and puts them on the Internet, so that people around the world can see them. Curiosity raw images are posted here, and the fastest way to get Opportunity images is from Exploratorium. Sometimes the whole process works so fast that you can see images on the Internet that were taken only a few hours ago on Mars.
In addition to the images themselves, there’s also information about the images, called metadata. Metadata includes things like the direction the rover’s camera was pointed when the image was taken, where the rover was located on the surface, and a description of the observation. This information allows apps like Midnight Planets to display full 360-degree views made out of the individual images. However, this information isn’t always included with the images that are posted on the web, so we have to look to a couple additional sites: for Opportunity the Pancam Tracking Database, and for Curiosity the Navigation and Ancillary Information Facility. More recently, json.jpl.nasa.gov became available. (And the best place to get Curiosity metadata for recent images would probably now be Curiosity JSON, but I haven’t had a chance to make use of that yet.) Without these websites, the data in Midnight Planets would be months out of date, or in some cases not available at all.
Every 15 minutes or so, an automated program at Midnight Planets headquarters scans the rover raw image websites for new images. This program is called Midnight Loader (and you can follow it on Twitter). Midnight Loader downloads any new images, checks for new metadata, processes it all into a package of data that works with the Midnight Planets app, and posts that to the web. When you run the Midnight Planets app, the app checks to see if any new data has been made available by Midnight Loader, and automatically downloads the new data as needed, ‘on the fly’.
At the same time that Midnight Loader updates the data for the app, it also updates the Latest Images pages, so that you can see the images that have come down most recently. The Latest Images pages display rows of thumbnail images which can be scanned quickly. You can tap a thumbnail image to see the full-size image and a little information about it, and from there you can view the image in the app.
The Midnight Planets image pages are optimized for Retina displays, as seen on some iPhones, iPod Touches and iPads, on Retina MacBook Pros, and (it is to be hoped) on more and more devices in the future.
Mars is a long way away, so it takes a lot of effort to get a radio signal from here to there and back again, especially since the rovers don’t have very much electrical power to send that signal. Even with the help of the satellites in Mars orbit, the amount of images and data we get from the surface of Mars on any given day is on the small side. That means that images have to be prioritized: it’s more important to get some images back right away, while others can wait until later. So sometimes we’ll see images show up that were taken a couple hours ago, and sometimes we’ll see images from weeks or months ago. That’s why the images on the Latest Images pages are divided into sections by sol, as well as by how recently they were downloaded.
Sometimes only thumbnail-sized images are available for an observation; again, this is because the low rate of transmission between Mars and Earth. The thumbnail-only images are shown at half width on the Midnight Planets image index pages, to visually indicate that they are smaller. These images are usually replaced by full-size images at a later time.
Midnight Planets has to collect images and metadata from different websites, and some of these websites are updated more frequently than others. For that reason, sometimes you will see images that have not yet been placed into a panoramic view in the app. Usually it all sorts itself out, given some time. In addition, the author of Midnight Planets makes some additions to the metadata himself, such as adjusting image brightness and adding descriptions of sites and sols.
We live in remarkable times, when humans guide robots to explore other worlds. Midnight Planets thanks the people at NASA/JPL who let us follow along on this journey.