Per the JPL website, there will be a presser on Monday morning, at 8:30 am PDT, which features several NASA science directorate types, but includes from current active JPL mission scientists only MRO/HiRISE PI Alfred McEwen. So I'm assuming the "major discovery" announcement was developed from MRO data.
The details are embargoed until 30 minutes prior to the presser, but the headline on the article is Mars Mystery Solved.
I'm looking forward to seeing what they have discovered.
-the other Doug