News

What Can We Actually Find on an Exoplanet? Part 3: Reading the Face of a Planet

(This is Part 3 of a series on what we can actually find on an exoplanet. Read Part 1 and Part 2 first.)

Oh, it’s enough. It’s never enough, of course, but it’s enough to justify building this monstrous planet-hunting telescope, because a single pixel gives you far more than you’d think. That dot has a color, maybe even a pale blue one. It has a spectrum. And it changes brightness as the planet spins on its axis and swings through its orbit.

The HWO is our first purpose-built biosignature machine. If life is common, meaning present on some meaningful fraction of habitable-zone rocky planets, the HWO will find it. And if it doesn’t, that tells us life is much rarer than we hoped. Either answer is worth having.

It helps that, to gather enough light, the HWO will have to stare at each planet for days to weeks. Every planet becomes its own project: months of preparation and planning, then weeks of observation, then a lifetime of analysis. That’s why studying just 25 worlds will take a decade. But because we watch each planet for so long, by the time we’ve built up a decent signal it has a lot to tell us. A lot more than atmospheres.

Back in 1990, Carl Sagan and colleagues talked NASA into pointing the Galileo spacecraft, then on its way to Jupiter, back at Earth for a look. The resulting 1993 paper, “A Search for Life on Earth from the Galileo Spacecraft,” is a classic. They deliberately analyzed the data as though they had no idea what planet they were looking at, treating Earth as an unknown target. They found oxygen and methane together, that classic cocktail in disequilibrium; an unexpectedly sharp jump in reflectivity at red wavelengths (hold that thought, it’s going to be fun in a minute); and a spray of narrow-band radio signals that no natural process could explain. That last one was us, blasting away across the radio dial.

That kicked off a whole tradition of using Earth as a test case, either by repurposing distant probes or by taking nearby ones and deliberately degrading their data, to see what Earth would look like to alien astronomers of various skill levels. And the theorists haven’t been sitting idle either. Bored theorists get creative, and they’ve dreamed up all sorts of ways to wring every last drop of information out of a bare pixel.

If you’ve ever seen sunlight bouncing off a lake at sunset, you’ve seen glint. It’s the mirror-like flash off a smooth, flat surface, technically called specular reflection, as opposed to the diffuse, matte scattering off dirt or sand or grass, which throws light in every direction. Water does the mirror trick. Land does not. Which means an ocean-bearing planet, seen from the right angle, should sparkle in a way a dry rocky planet simply can’t.

The right angle turns out to be crescent phase, when we’re seeing the planet mostly from its night side with just a thin sunlit sliver showing, the way we see a crescent Moon. In that geometry, sunlight skips off the ocean at a steep grazing angle and heads more or less straight back at us, and the whole crescent lights up like a mirror. Simulations show that ocean glint can nearly double Earth’s total brightness at crescent phase. That’s the difference between a wet world and a dry one, sitting right there in how the planet’s brightness changes as it goes about its business.

Better still, the glint isn’t steady as the planet turns. When a continent rotates into view it interrupts the mirror bounce and the glint dims; when ocean swings back around, it brightens again. The planet appears to blink. And that blinking is a fingerprint of a partly oceanic surface that you can’t fake with clouds or ice caps alone.

Push it further. If you can watch an exoplanet through one full rotation, one of its days, however long that lasts, and track how its total brightness changes as different parts of the surface turn into view, you can mathematically invert those brightness swings to reconstruct a rough map of what lies at which longitudes. Bright deserts, dark forests, blue oceans, white ice caps: each reflects differently, and each rotates into view at a different moment. Measure the brightness changes precisely enough and you can back out where each kind of surface sits on the globe. From brightness alone. Without ever resolving the planet as anything more than a single point.

Stretch the same technique across months and multiple orbital phases, so the tilt of the planet’s axis brings different latitudes into view at different times, and you can start recovering crude two-dimensional maps, latitude and longitude both. This too has been done for Earth, using data from a let’s-pretend-this-is-a-distant-alien-telescope satellite, and the recovered maps show recognizable continents. From a single pixel.

So we can pull out oceans, continents, shapes. And vegetation. Chlorophyll, the molecule that makes plants green, absorbs red and blue light greedily (that’s the light it eats) and reflects green (which is why leaves look green: the green bounces back to your eye). But something remarkable happens just past the red end of the visible range, in the near-infrared. Plant leaves suddenly become extremely reflective. Not for photosynthesis, since near-infrared photons don’t carry enough energy to power the chemistry anyway, but as protection, so leaves don’t soak up too much heat and cook themselves. The switch from absorbing red to reflecting near-infrared happens across a very narrow band of wavelengths, right around 700 nanometers.

Plants go from absorbing most of the red light that hits them to reflecting most of the near-infrared, a jump of a factor of five or more, across a stretch of the spectrum narrower than the width of a laser pointer. This feature is called the vegetation red edge, and it is genuinely bizarre. Nothing else in nature, no rock, no mineral, no ocean, no cloud, no atmospheric molecule, produces a step this sharp at this wavelength.

Which means that if we ever spotted a red-edge-like feature in the reflected light of an exoplanet, a sudden sharp jump in reflectivity at a specific wavelength, we’d have compelling evidence for surface photosynthesis. Forests. Or the alien equivalent. The catch, and it’s a real one, is that even on Earth the red edge is only a few percent of the total reflected light, because plants cover only about 60 percent of the land, land covers only about 30 percent of the surface, and clouds blanket about half of everything at any given moment. The signal gets badly diluted. But it’s still there, and the HWO would be sensitive enough to catch it on a nearby world if plant-like life is abundant.

The really fun part arrives when you add seasons. On a planet with axial tilt like Earth’s, covered in deciduous forests, the strength of the red edge should rise and fall over the year, growing as leaves come out in spring and summer, weakening in fall and winter. A world whose red edge swelled and shrank in step with its orbit would be a world whose surface was thriving in summer and hunkering down in winter. That would be one of the most stunning biosignatures imaginable: not a static chemical fingerprint, but a dynamic one, keyed to the planet’s seasons.

Of course, alien plants don’t have to be green. Plenty of photosynthesis on Earth is done by red algae, so we don’t have to fixate on this exact wavelength. But if we see sharp features in the spectrum shifting as the planet moves through its seasons, that is big.

In Part 4, we go looking for something even bolder than life in that single dot: the smokestacks of an alien civilization.

News

San Diego supervisors kick ICE out of county-owned shooting range

?url=https%3A%2F%2Fcalifornia times brightspot.s3.amazonaws.com%2Fdc%2F7e%2F7a8ad0e5433692602da2b9a4db5a%2Fme san diego regional firearms training center

A showdown is shaping up between San Diego’s Board of Supervisors and the Sheriff’s Department over whether federal immigration agents should be allowed to continue firearms training on a shooting range owned by the county.

On Tuesday, the board voted 3-2 to terminate agreements with Immigration and Customs Enforcement and Customs and Border Protection over both agencies’ use of the San Diego Regional Firearms Training Center in Otay Mesa.

However, Sheriff Kelly Martinez swiftly intervened. She said that although she supports ending ICE’s firearms training at the site, she will allow CBP to continuing using the shooting range for training. It’s unclear how the conflict will play out.

The supervisors who voted in favor of terminating both ICE’s and CBP’s access to the range argued that agents’ use of the facility threatens the community’s trust in local government, following concerns over use of force during the Trump administration’s immigration crackdown.

However, the Sheriff’s Department, CBP, and the San Diego Regional Chamber of Commerce all expressed concerns that kicking CBP agents out of the training center would lead to longer wait times at the border and San Diego International Airport and hurt the local economy.

“CBP officers must be able to complete this [firearms] training efficiently and quickly return to their duties at the border ports of entry, cruise ship terminals, and the airport,” the Sheriff’s Department said in a statement Tuesday. “Without this ability, [border] lanes will close and wait times will be extended.”

The supervisors who wrote the motion, Paloma Aguirre and Terra Lawson-Remer, say that lengthy waits at the border are the responsibility of the federal government.

“I share our business community’s commitment to short lines and a thriving border,” Aguirre told the San Diego Union-Tribune. “The real threat to that economy is a federal government that pulls CBP officers off the lanes to run raids in American neighborhoods.”

Sheriff Martinez said Tuesday that although ICE’s primary mission is enforcing federal immigration law, CBP is focused on safeguarding borders and economic prosperity at ports of entry.

“Too many people on both sides of the border would be harmed by a decision to end CBP’s use of the facility,” Martinez said. “As sheriff, I have a duty to protect and serve everyone who lives in or enters San Diego County.”

Supervisors Aguirre and Lawson-Remer, however, pointed out that CBP agents have been heavily involved in the Trump administration’s mass deportation campaign.

They said that increased immigration enforcement had led vulnerable families in San Diego County to fear that accessing public services would expose them to deportation.

“When County facilities are used by federal immigration enforcement agencies, that fear is compounded, making it harder for residents to seek medical care, report crimes, enroll children in school, or engage with local institutions,” the item states.

Aguirre and Lawson-Remer could not immediately be reached for comment on what actions might be taken in the wake of the sheriff’s opposition.

The board vote was split along party lines, with Democratic Supervisors Aguirre, Lawson-Remer and Monica Montgomery Steppe in favor, and Republican Supervisors Jim Desmond and Joel Anderson in opposition.

The agenda item noted that ICE agents removed more than 16,000 people from San Diego County between January 2025 and April 2026. It also stated that there had been at least 41 shooting incidents, resulting in 11 fatalities, involving federal immigration agents during Trump’s second term.

Most of those shootings have involved ICE agents; there have also been instances, however, where CBP agents’ use of force has been questioned.

In August 2025, for example, CBP agents opened fire at a vehicle carrying a man and his 18-year-old son while conducting a traffic stop in San Bernardino. CBP alleged that the dad accelerated toward officers, but federal prosecutors later dropped all charges filed against him.

Since 2024, ICE and CBP have logged about 3,350 training hours at the San Diego Regional Firearms Training Center, according to the county.

ICE and CBP entered the license agreements to train at the Otay Mesa site in 2021, with ICE paying the county about $10,000 a year and CBP paying about $117,000. ICE also entered a separate agreement with the county in 2022 to use a firing range on Marine Corps Air Station Miramar, which is owned by the Navy and leased to the county.

Neither agreement initially came before the board for a vote, because the amount of money involved was small enough for them to be approved administratively. An April investigation by local news organization iNewsource brought the agreements into public light, prompting the debate over whether they should be allowed to continue.

A similar debate played out in February over ICE agents’ use of the the city of Escondido’s firing range. However, in that case the City Council opted to uphold its contract.

News

Frank Beard, Beardless Drummer for ZZ Top, Dies at 77

The only member of the Texas power trio without a beard, he propelled the band’s blend of boogie, Southern rock and blues for more than a half-century.

News

What Can We Actually Find on an Exoplanet? Part 2: A Machine to Find Another Earth

(This is Part 2 of a series on what we can actually find on an exoplanet. Read Part 1 first.)

It’s not hopeless, because the James Webb isn’t the last telescope we’ll ever build.

Next up on the docket of space launches is the Nancy Grace Roman Space Telescope, which will mostly run deep-universe cosmology surveys but will also, almost incidentally, pick out millions of exoplanets using a trick called microlensing. That only reveals that a planet exists, not whether it can support life, which is very cool but not our subject today.

Our subject today is what comes after that: the Habitable Worlds Observatory. It’ll surely be renamed after someone famous eventually, but for now it’s a little more than a sketch in a notebook. The HWO is like a super-James Webb, and the James Webb was already a super-Hubble, which makes this a super-duper Hubble. And despite a planned mirror actually a touch smaller than the James Webb’s, it carries one instrument that earns it the title of biosignature hunter: a coronagraph.

A coronagraph is a very simple device that has to be built almost impossibly well. It’s basically a bit of metal shaped to blot out the light of the parent star while you look at the system around it. You know how you cover the Sun with your thumb to see something near it in the sky? It’s like that, except that to reach the precision it needs, it actually uses a series of exquisitely shaped masks that exploit the wave nature of light. The starlight is made to destructively interfere with itself and cancel out at exactly the spot where the planet’s light is slipping through untouched.

The whole point is to stop relying on filtered starlight to do our dirty work and instead get a picture of the planet itself, in all its reflected-light glory. And this is an undertaking, to put it mildly. To directly image an Earth-like planet around a Sun-like star, you have to pick out something roughly ten billion times fainter than the star sitting right next to it. Picture standing on a beach in California and trying to spot a single match being struck next to a lighthouse in Japan. The star is firing ten billion times more photons at you, at every wavelength you care about, than the planet is, and essentially all of the HWO’s design effort goes into building a coronagraph that can pull the planet out of that glare.

The HWO is not a survey telescope. It’s not a scanner. It’s a hunter. Its stated goal is to find and directly image at least 25 potentially habitable worlds and take their pictures. Hubble was a general-purpose observatory. The James Webb was built for early galaxies first and exoplanets second. Every choice about the HWO, the mirror size, the coronagraph, the wavelength range, the stability requirements, was made with “find life on another world” sitting at the top of the list.

But to reach that kind of precision, to hit the contrast level where we can actually pick out the fine details of a planet’s light, the mirror has to hold its shape to within picometers. That means the whole telescope, floating in space, buffeted by temperature swings and the vibrations of its own machinery, has to stay stiller than the jiggling of individual atoms. If you blew the HWO mirror up to the size of the continental United States, keeping it stable to picometers would be like holding that entire surface flat to within the width of a human hair.

I’ll be honest with you: we don’t currently know how to do this. That’s why, even though it’s about the same size as the James Webb, the HWO is a generation-scale engineering problem, and why it won’t launch until the 2040s at the earliest.

Which is fine, because hunting biosignatures isn’t only a technology problem. It’s also a theory problem. Even with perfect data, we’d hit a wall, because to turn a spectrum into “here’s how much of each gas is in this atmosphere,” we need reference tables built from laboratory measurements and theoretical calculations: how much light does methane absorb at 3.3 microns, at what temperature, at what pressure, mixed with what other gases. These are called opacity models, because of course they are.

Imagine you’re a bartender trying to identify a mystery cocktail by taste alone, except your recipe book was written by someone who tasted each ingredient one at a time, at room temperature, and never actually mixed anything. Now you’re handed a drink that’s been chilled, shaken, and blended with five other flavors. Your recipe book is technically correct, the best kind of correct, but the actual taste in your mouth is doing things the book never anticipated. Sometimes you can’t even tell if that’s gin or vodka.

That’s roughly where we are with exoplanet atmospheres. We know how methane absorbs light at room temperature in a lab. We know how water does. We don’t really know what happens when both sit at 700 Kelvin and ten atmospheres of pressure, mixed with hydrogen and traces of a dozen other gases, billions of molecules deep. There’s so much uncertainty in these models that ten astronomers could look at the exact same spectrum and walk away with eleven different interpretations, some of them thrilling hints of life and some of them nothing at all. This is why we keep getting headlines about big biosignature discoveries, only for those studies to be quietly walked back a few months later when nobody’s watching. The devil is in the details, and with biosignatures it is all details.

But we’ve got time, a couple of decades, to sort it out before the HWO starts pointing at planets and telling us what they’re made of. And yes, you heard me right: about two dozen candidate planets, total. We’re putting a lot of eggs in one basket, because honestly it’s the only basket current technology gives us, and even that is stretching the meaning of “current technology.”

And all of that, for our first pictures of potentially habitable worlds to amount to a single pixel of light.

Is that enough?

In Part 3, it turns out one pixel is enough for a shocking amount, as we learn to read oceans, continents, and even forests off a single point of light.