Comet nuclei are typically small, often less than a mile across. However, NASA’s Hubble Space Telescope recently observed a behemoth: Comet C/2014 UN271 (Bernardinelli-Bernstein). Just how big is this comet compared to Earth? While not Earth-sized, its nucleus is a staggering 80 miles in diameter, larger than the US state of Rhode Island. To put that in perspective, it’s roughly 50 times larger than most known comet nuclei.
A Comet of Colossal Proportions: Size and Distance
Comet Bernardinelli-Bernstein’s massive size is matched by its incredible mass: an estimated 500 trillion tons, a hundred thousand times greater than a typical comet. While travelling at 22,000 miles per hour, it poses no threat to Earth. Its closest approach to the Sun in 2031 will still be over 1 billion miles away, farther than Saturn’s orbit.
Before this discovery, the largest known comet was C/2002 VQ94, with a 60-mile diameter nucleus. Bernardinelli-Bernstein shatters that record, highlighting the vastness and mystery of the Oort Cloud, the comet’s likely origin.
Measuring a Distant Giant: Hubble’s Role
Determining the size of such a distant object was a challenge. Hubble couldn’t directly resolve the nucleus due to the vast distance and surrounding coma. Instead, scientists analyzed the light spike from the nucleus, creating a computer model of the coma to isolate the nucleus and estimate its size and reflectivity.
Combining Hubble’s data with previous radio observations from the Atacama Large Millimeter/submillimeter Array (ALMA) confirmed the enormous size and revealed a surprisingly dark surface, “blacker than coal,” according to researchers.
Journey from the Oort Cloud: A Comet’s Origins
Comet Bernardinelli-Bernstein originates from the Oort Cloud, a theoretical sphere of icy bodies surrounding our solar system, thousands of times farther than Earth’s distance from the Sun. Gravitational disturbances from passing stars can send these icy objects hurtling inwards, like this comet on its 3-million-year elliptical orbit.
The comet’s discovery offers valuable insights into the Oort Cloud’s size distribution and mass, a region too distant for direct observation. Though still a theory, the Oort Cloud is thought to hold trillions of comets, remnants from the early solar system.
Significance and Future Research
This record-breaking comet provides crucial clues about the solar system’s formation and evolution. Further studies of Bernardinelli-Bernstein and future discoveries from deep-sky surveys will enhance our understanding of the Oort Cloud and its role in shaping our cosmic neighborhood.
