Sightings with the Spitzer Space Telescope show that it 's diameter is about 70 km ( 43 miles ) plus or minus 20 km ( 50 to 90 km in diameter ) , or a 35 km radius . Observations with the infrared Spitzer Space Telescope show a diameter of 10370 to be 70 km ( 43 miles ) plus or minus 20 km ( 50 to 90 km in diameter ) , or a 35 km radius .