CRISM Team Closing Operations With New Global Map of Mars

Tue, 06/21/2022 - 17:27
Jeremy Rehm

Get ready to see Mars like never before.

The team behind the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on NASA’s Mars Reconnaissance Orbiter (MRO) spacecraft released the first pieces of a new near-global map of the Martian surface on June 15 — a massive 5.6-gigapixel image in 72 colors, conveying the mineral composition of the Martian surface.

Made up of roughly 51,000 540-kilometer-long strips that together cover nearly 86% of the Martian surface, the map is the first of its kind, providing new context and a trove of data that the team expects will spawn new findings about the red planet for years to come.

“It’s effectively a whole new data set that will fuel a second wave of discoveries about Mars’ surface composition,” said Scott Murchie, a planetary scientist at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, and CRISM’s principal investigator. “In fact, one of the objectives of the next MRO extended mission is for its HiRISE camera to go back and image in color the hundreds of new high-science priority spots we’re finding in the map — spots that haven’t been imaged at high resolution because their importance wasn’t known.”

The team released 48 of the map’s 1,764 tiles to NASA’s Planetary Data System (PDS) on Wednesday, a down payment that covers five of the most scientifically interesting regions of Mars. The team plans to release the remaining 1,716 segments in batches over next six months to interleave with the routine MRO deliveries to the PDS.

Built and operated by researchers at APL, CRISM has been primarily searching for mineralogical evidence of water that once existed on Mars billions of years ago by capturing images in up to 544 different colors (or wavelengths) of reflected visible and infrared light. It exploits the fact that minerals each have molecular structures that produce unique “fingerprints” in reflected light, which scientists can readily recognize and piece together.

Over the years, CRISM has made a name for its roughly 33,000 high-resolution targeted observations, each of which covers just about 6 × 6 square miles (10 × 10 square kilometers) of Mars’ surface in all 544 colors. These images played a major part in the selection of landing sites for Mars rover missions and in making the Mars Sample Return mission a high priority, thus fueling a huge wave of future discoveries.

But for nearly 11 years, the instrument also collected roughly 83,000 lower-resolution mapping strips — image scans that are each up to 335 miles (540 kilometers) long, 6 miles (10 kilometers) wide, and composed of just 72 colors, providing local and global context unavailable in the higher-resolution targeted observations.

Through fits and starts over the course of the mission, the CRISM team worked to develop the data-handling procedures that could sew the thousands of individual pieces into cohesive maps, running each strip through a lengthy data processing and rigorous optimization process to account for environmental variations, such as differing weather conditions, and intrinsic discrepancies among the constituent pieces.

“For an individual tile, the optimization process might take just five hours in some exceptional cases, but sometimes it will take over a day,” said CRISM team member Katie Hancock, a software developer at APL who spearheaded the development of the optimization code. Building a map of the entire planet, she said, takes a computer cluster closer to a month.

The team has produced 48 map segments thus far, each of them composed of dozens of individual mapping strips acquired over many years and under various conditions. The product set for each tile includes a collection of data visualization maps, each of which reveals something different about the mineral composition of Mars.

“We’ve had the map tiles as a product set on the books really from the very beginning,” said Frank Seelos, a planetary scientist at APL and lead on the CRISM mapping project. “We knew we wanted to do this, but it took us many, many years to get to the point where we had enough data and the tools needed to make it worthwhile.”

The timing of the map tile product release is also notable. The instrument’s cryosystem was retired in 2018, effectively precluding the instrument from collecting any more infrared data, and CRISM is now headed into its closeout phase. The team finished the last planned data acquisition in May, although the instrument will remain operable in case a discovery warrants a closer look with CRISM.

“The warranty on this thing expired years ago, before my kids were even born,” Seelos said, chuckling. Having been on the mission since its launch, it’s still bittersweet for him and for many others. “The CRISM investigation has been very long-lived, and the fact that we were able to take data for so many years is amazing. The release of these tiles is a kind of exclamation point for the instrument’s legacy.”