Stellar passage of HD 7977 likely triggered a comet shower in our solar system

Star system: HD 7977 | Distance from the Sun: 247 light years

Long-period comets, which take thousands of years to orbit the Sun, are traditionally thought to be nudged toward the inner solar system by the gravitational pull of the Milky Way's disk. New evidence suggests that the star HD 7977 may have passed close to our solar system 2.5 million years ago, creating a "comet shower" that continues to influence the number of comets we observe today.

The research compared computer simulations of long-period comets with their observed paths. While the standard model of galactic influence failed to perfectly match the data, adding a flyby of HD 7977 within 6,000 to 10,000 astronomical units—one astronomical unit is the distance from Earth to the Sun—provided a much better fit for the observed distribution of these comets.

This gravitational encounter suggests our solar system is in the final stages of an influx of comets. If accurate, this implies that the number of comets entering our neighborhood is currently double the long-term average, and the total population of the Oort cloud—a vast, distant region of icy objects surrounding the solar system—may be half as large as previously estimated.

Key findings
- The star HD 7977 likely passed within 6,000 to 10,000 astronomical units of the Sun 2.5 million years ago.
- This flyby explains the current distribution of new and returning long-period comets better than galactic tidal forces alone.
- The current flux of long-period comets is estimated to be twice the long-term average.
- Oort cloud population estimates may need to be revised downward by a factor of two.
- Future data from the Gaia space observatory is expected to confirm the specific path of HD 7977.

Scientific study

A Potential Signature of HD 7977's Passage Among Observed Long-Period Comet Orbits (external link)