Welcome to this week’s AITN Lite and the first of the new academic year. As always, I try to link these to the previous week’s bulletin, and having picked three science stories last week, I had lots of choice. One of the JWST images highlighted last week was a planetary nebula from the death of a star. This week is about a planet that has survived the beginning of the death of its host star. The article can be found here:

https://www.bbc.co.uk/news/science-environment-66042269

The planet, 8 Ursae Minoris b, is orbiting a helium-burning red giant. A helium-burning red giant is formed when a main sequence star runs out of burning hydrogen, and the core contracts. This contraction leads to the expansion of the star, but gravitational collapse in the core will cause a hydrogen burning shell. This causes further stellar expansion, and once the hydrogen is exhausted, collapse occurs in the core and expansion of the star continues. This core contraction causes helium burning to begin. This expansion, in the case of the Sun, would expand to nearly Earth and, at the very least, engulf Mercury and Venus.

This is the fact that makes 8 Ursae Minoris b such an interesting planet. It has a relatively close orbit of 0.5 astronomical units (the distance between the Earth and the Sun; AU), but the expansion of the star should have taken this star out to 0.7 AU. The fact that the planet is still orbiting means that it can’t have been engulfed. An explanation that scientists have come up with is that this star was once a binary system. When the star has expanded, it has engulfed its companion star first. This companion star, a white dwarf that was burning helium, has allowed the helium burning to start in the red giant, and has stopped its expansion, given 8 Ursae Minoris b a reprieve!

Curriculum topics to be considered
Stellar life cycle