There were multiple different alpha versions, 1.2 being the last uncut alpha version.
Fig update[]
The previously available alpha was replaced with a cut-down alpha demo at the start of the Fig campaign that successfully funded development of the full version.
Spoiler bubbles[]
Dark Bramble, Giant's Deep, the Hourglass Twins and the Quantum Moon were blocked off by huge bubbles covered with a warning message "Danger - spoilers ahead". Entering any bubble and not leaving it again within 5 seconds makes the sun explode instantly, killing the player within a few seconds.
Besides that, these planets appear to be unchanged compared to the previous full alpha.
There's no known way of bypassing the bubbles - using the probe is not an option either as it's strongly repelled. Of course it's possible to enter any such bubble at high speed for getting a short glimpse of the planet.
Sun Station[]
A Sun Station was added which was not present in the previous alpha version. It's much smaller than the one in the release version and seems to only consist of a single platform with a spiral-like structure underneath.