Hubble and GJ 436b: the planet trailing a hydrogen cloud, with timestamps
Giant planets can conceal rocky cores and exotic interiors beneath their clouds.
Source: NASA Science, “ScienceCasts: Worlds within Worlds” · Public domain: US government work (NASA)
A Neptune-sized planet is losing its atmosphere into a cloud larger than its star. Here is what NASA's ScienceCast says, line by line. The source is NASA Science's video “ScienceCasts: Worlds within Worlds” (3:51). Every claim below links to the second it was said, so you can check it in a click.
In short
- Giant planets can conceal rocky cores and exotic interiors beneath their clouds. 0:29
- A star’s radiation is stripping hydrogen from GJ 436b, potentially leaving behind a Hot Super-Earth. 2:30
- Ultraviolet observations can reveal escaping atmospheres and may even detect evaporating oceans on Earth-like planets. 3:27
Key moments
| Time | What happens | In their words |
|---|---|---|
| 0:29 | Neptune and Uranus each hide a rocky core beneath their cloud tops. | “Hidden deep below the azure cloud tops lies a rocky core not much larger than Earth. Uranus has one, too!” |
| 0:55 | Astronomers discovered a huge hydrogen cloud escaping from GJ 436b. | “Astronomers using NASA's Hubble Space Telescope have discovered an immense cloud of hydrogen evaporating from a Neptune-sized planet named GJ 436b.” |
| 1:39 | The planet may have lost as much as a tenth of its atmosphere. | “"Overall, we estimate that the planet may have lost up to 10 percent of its atmosphere."” |
| 2:30 | The Behemoth’s existence supports the idea that Hot Super-Earths are stripped Warm Neptunes. | “The existence of The Behemoth suggests that Hot Super-Earths could be the remnants of Warm Neptunes that completely lost their gaseous atmospheres to evaporation.” |
| 2:39 | Hubble’s ultraviolet vision reveals the cloud that visible light cannot show. | “Finding a cloud around GJ 436b required Hubble's ultraviolet vision.” |
Worlds Inside Planets
Look beyond Neptune’s blue exterior: it contains a rocky core not much larger than Earth. 0:29
Remember that Uranus also has a hidden rocky core. 0:29
Consider that these hidden worlds may have scorching hot oceans and diamond rain. 0:36
Note that researchers have found a Neptune-sized planet about 30 light years away with layers being peeled back. 0:48
“They say you can't judge a book by its cover. But what about planets?” 0:12
The Behemoth and Evaporation
GJ 436b is losing hydrogen as intense radiation from its parent star evaporates its atmosphere. 1:17
The star was more active in the past, so the planet may have lost up to 10 percent of its atmosphere. 1:39
The Behemoth may help explain Hot Super-Earths as the stripped remnants of Warm Neptunes. 2:30
“This cloud is spectacular,” 1:06
Ultraviolet Exoplanet Observations
Use space-based ultraviolet observations to detect features that visible-light observations can miss. 2:45
Ultraviolet light reveals the Behemoth because it is opaque to UV rays despite being transparent in visible wavelengths. 2:59
Look for evaporation on warm Neptunes, Super-Earths, and potentially Earth-like planets. 3:23
“Finding a cloud around GJ 436b required Hubble's ultraviolet vision.” 2:39
How this post was made
BlogPen wrote a note from the video's transcript (note:v1, 2026-11-05); this post sets that note out as prose without adding facts. Source licence: Public domain: US government work (NASA). https://www.youtube.com/watch?v=TbWX7-ZoJAk
Make the same kind of note from a video you need: YouTube to notes, or take it further with a blog draft.