I've heard of them.
Imperial College of London is a very well respected research university in the geology field. I know this as a professional geoscientist myself they have 14 Nobel laureate from when Nobel prize meant actual science not politics.
An impact of a astronomical body of this size would throw billions of tons of molten material into not only the stratosphere but a good portion would have orbital velocity and enter low earth orbit. Over the next weeks that material would reenter and burn up adding further particulates to the upper atmosphere blocking sunlight for years leading to massive curtailment of photosynthesis and the collapse of every global food web. An impact of this size would also create materials with escape velocity and put matter into solar orbit especially at a glancing blow. Just for reference there are meteorites found on Earth that have been traced to Mars blasted here by impacts on Mars in the past into solar orbit and then captured by earth’s gravity well. Fascinating stuff as it’s the only direct sampling of Martian material humans have until a sample return mission is conducted....come on falcon heavy! Which has more than enough throw weight to put a sample return mission to the C3 delta V needed.