Senior research scientist Ted Scambos with the University of Colorado at Boulder says the iceberg is in the ballpark of 40 metres tall and anywhere from a mile or two long.
The ice shelf is about 1,100ft thick and floats on the edge of West Antarctica. Tabular icebergs are more common than people realise.
"This one came from the crumbling Larsen C ice shelf on the Antarctic Peninsula". At that point, tides or strong winds could break icebergs off.More news: More than 20 injured in Rome escalator collapse
Nasa had found a piece of floating ice in Antarctica that is so flawless, it looks like it was deliberately cut.
"The best thing I can say is that when a "trillion tonne" iceberg runs into an ice-covered rocky island (Bawden Ice Rise) the crystalline glacier ice will fracture along planes of weakness, much like a more typical mineral crystal might be cleaved". The chunk of ice has since been known as iceberg A-68.
But why such straight lines? By contrast, iceberg A68's surface area measured some 2,240 square miles at the time of calving.
The study is the largest airborne survey of Earth's polar ice ever flown, taking 3-D images and keeping track of sea ice thickness. In the past, these flights have mapped Greenland's ice sheets, identified collapsing ice shelves, and spotted mysterious holes in the Antarctic ice.
"IceBridge and ICESat-2 both use laser altimeters that fire pulses of light toward the ground and measure how long it takes for that light to bounce off the ice and return to the instruments' sensors", NASA said earlier this month.