Michelle Thaller

The episode opens casually. One speaker describes trying to explain black holes to high school students that week, and mentions a recent astronomy talk for the Men's Club in Shorewood, Wisconsin, whose members were excited to hear about this podcast appearance. The conversation then turns to that speaker's public science work. They describe a career at NASA spent largely as a science spokesperson, appearing in NASA videos and hosting launch events, with little private YouTube work so far, though they are considering starting some.

The first scientific thread is scale. The discussion tries out a comparison from earlier talks: if the Sun were the size of the dot on an "i" on a page of text, the Milky Way galaxy would be bigger than the Earth. The transcript wobbles on the details. At one point the comparison is phrased as the galaxy being "the size of the earth," and the Earth and Sun are briefly confused before the Sun is settled on as the reference dot. Supporting figures follow: more than a million Earths would fit inside the Sun by volume, the Sun is about 800,000 miles across, and a light year, the distance light travels in a year, is about six trillion miles.

The point of the numbers is that they fall short. Professionals get used to the terms and figures, but the discussion insists that their intuition is no better than anyone else's:

Nobody can visualize what a galaxy really is.

The James Webb Space Telescope is offered as the corrective. Its images capture billions of galaxies, which appear as foggy hazes of stars too numerous to resolve one by one. The argument is that a photograph is direct evidence and "not something that you can argue about."

After a short remark that the best part of NASA was the joy, teamwork and camaraderie of people who thought the work was the best thing in the world, the conversation moves to light pollution. Cities and electricity are described as good things. Even so, losing a regular view of the stars is called a "massive disservice." When people see the sky only as phone images or on vacation, the discussion argues, they lose the wonder, even though the Milky Way overhead is "the most spectacular thing any human being has ever seen." People become dismissive of something that is above them every night. One speaker urges more people to get away from cities and see that "we're flying through space," and notes that no telescope or binoculars are needed.

The conversation then argues that humans are part of what they see when they look up, not separate from it. The basis is nucleosynthesis as stated in the source: aluminum, iron, oxygen, carbon, phosphorus and the other elements in our bodies were forged by nuclear fusion.

You know, the only thing in the universe that makes atoms is the interior of a star.

From this the discussion calls astrophysics the story of "the end of your nose, literally." The participants link the idea to the lyric "we are star-dust... we are gold" and "got to get ourselves back to the garden." They also note that this detailed understanding of the universe is recent in human history and has been pushed further by the James Webb Telescope.

The early galaxies seen by Webb come up as something that puzzles researchers because they appear to have formed so early. One speaker mentions giving a talk on them a few weeks earlier. The discussion does not explain why they form early. Instead it moves to their name, "the little red dots," as an example of plain astronomical naming. Jupiter's Great Red Spot is another: a storm described as three times the size of Earth with 400-mile-an-hour winds, still called "the red spot."

The explanation given is procedural. Someone who discovers an asteroid gets to name it, and a comet is named after its discoverer. Anything else goes through an international committee, so most objects end up with catalog numbers, which are described as "basically phone numbers."

The hexagon at Saturn's pole, briefly misplaced on Jupiter, gets a fuller treatment. It is described as a hexagonal jet stream of very fast winds around the pole, about two Earths across. Because Saturn's gas is so cold, there is "almost no friction in the gas." The discussion highlights a Cassini image of the storm's eye that shows sunlight glinting off cloud banks hundreds of miles high, and stresses that "we went there. We flew over that storm."

The proposed mechanism is a standing wave set up in the jet stream's circulation, which produces the hexagonal shape when heat and friction are removed. It is compared to persistent patterns in Earth's jet stream, which make the weather a week out look much like today's. The explanation comes with a stated limit, "I'm not an atmospheric specialist, but that's what I know," and with the evidence that computer simulations of fast jet streams under Saturn-like conditions can reproduce the shape.

Saturn is described as "right in our neighborhood," though hard and slow to reach. The next topic is NASA's planned mission to Titan, which the discussion hopes will launch around 2028 and take six or seven years to arrive. Titan is described as having a thick atmosphere, with surface pressure slightly greater than in the studio, temperatures close to 300 degrees below zero, many organic molecules, and evidence of liquid water below the surface. For these reasons it is called one of the places "that might be friendly for life."

The mission, Dragonfly, is described as a large octocopter drone carrying a chemistry laboratory to look for conditions for life. Because it can fly, it could sample more than one site. Titan has rain, rivers and open lakes the size of the Great Lakes. These are not water but liquid natural gas, which the discussion identifies as methane. The conversation recalls that a probe from the Cassini mission already landed on Titan, took readings and "eventually froze to death." Some of those readings are described as "intriguing" for the possibility of life, but no specifics are given.

Venus is the contrast case. The Soviet Union is described as the only nation ever to land on Venus, more than once, and landing there is called "way hard." The figures given are a surface temperature of about 1,000 degrees and air pressure similar to being about a mile below the ocean. The landers' real photographs show a landscape "crushed flat" under a dense atmosphere, with yellow-tinted sulfuric acid clouds, a "classic vision of hell." The landers did not last long.

The variety among the solar system's planets leads to a question: could planets elsewhere be set up completely differently? The answer is "absolutely." The count of known exoplanets changes daily and is given as roughly 5,000. One speaker traces their involvement back to college, when their research advisor, David Latham, was trying to find the first evidence of planets around other stars. Planets are tiny and dark and only reflect starlight. Finding them was compared to trying to see a firefly next to a searchlight from 200 miles away. New planets are now found almost daily, and the discussion predicts thousands per year soon.

Most exoplanets have not been directly imaged because they are "smaller than a pixel." They are found by transits: a planet passing in front of its star makes "a tiny little solar eclipse" that blocks a little starlight. The discussion gives a standard of evidence. The dimming must recur three times before it is called a planet, because otherwise it could be a spot on the star or something else. Starlight passing through the planet's atmosphere also lets researchers probe its chemistry. Some planets around the size and temperature of Earth show evidence of water vapor, carbon dioxide and oxygen.

The most heavily qualified claim in this section is a James Webb Space Telescope press release from the previous year. It reported possible signs of organic molecules that some scientists thought might someday be linked to life, resembling something plankton might give off on an ocean world. The discussion calls it controversial, says "We need to follow it up," and says the signal is not very strong yet. It also gives the counterposition directly:

And then, of course, the rest of the scientist said the data is not good enough yet.

The cautious reading offered is that it might be an organic carbon-based molecule whose identity is still unknown, and the advice is to "stay tuned." One speaker adds that they never expected the first hard chemical evidence of life beyond Earth might come from a planet around another star rather than Mars or the moons of Jupiter and Saturn. Webb and later telescopes might make that possible.

Asked how light passing through such a small target can be analyzed, the discussion explains spectroscopy. It notes that most scientists work less with beautiful images than with "little squiggly lines." Light is passed through a grating that spreads it into a rainbow, like the prism on Pink Floyd's Dark Side of the Moon cover. Measuring carefully how much light arrives in each color reveals a star's temperature, how fast it rotates, in some cases a galaxy's distance, and its chemistry molecule by molecule.

Every element, carbon, nitrogen, oxygen has a fingerprint in the rainbow.

These fingerprints also exist for water vapor, carbon dioxide and organic molecules. That is how starlight filtered through an exoplanet atmosphere can be read. An image of a luminous dying star in what the transcript renders as the "Karena Nebula" illustrates the method.

Helium is the historical example. Named after the Greek sun god Helios, it was identified in sunlight passed through a prism in the late 1800s as a pattern matching no known chemical. Only later was it found on Earth, in natural gas and from radioactive decay. The discussion explains that helium is so light it escapes the Earth. The participants look up the date and give 1868, and credit a French astronomer whose name is transcribed as "Pierre Jean-Saint." They admire that people in 1868 could work this out at all.

The conversation turns to Einstein's work on time, dated to around 1908, more than 100 years ago. The discussion notes that physics still has no better framework. The opening question is about GPS satellites. The speed first suggested, about 20,000 miles an hour, is corrected later. The discussion says NASA calibrates the GPS satellites and their signals, and that without correcting for their time difference, positions would be about six miles off within a single day.

Time is variable depending on how fast you're going and also how far off the Earth's surface you are.

This is then refined to how far you are from a large source of gravity. The gravitational effect is described as measurable over very short distances. Clocks are accurate enough to detect time flowing differently after being raised about two feet. A standing person's head and feet therefore move through time at slightly different rates. Interstellar's black hole is the extreme version of the same effect, and the discussion stresses that it is measured with clocks and is "not a theory."

Two effects push in opposite directions, and which one wins depends on the orbit. GPS satellites are in a medium orbit, below geostationary satellites. Their speed is given as about 9,000 miles an hour and later as 8,000, an inconsistency in the source. Their speed slows their clocks, but the larger effect is their distance from Earth's gravity, so their time runs a little faster than time on the ground. Astronauts on the space station are closer to Earth and move faster, roughly 20,000 miles an hour by the discussion's estimate, so motion dominates. A year on the station is said to return someone about one hundredth of a second younger than expected, "not a big deal, but it's easily measurable." For GPS, both effects must be accounted for to get correct locations.