Artist's concept of the four planets of the V1298 star system. Credit - NAOJ's Astrobiology Center
Have you ever wondered what planets look like when they're just born? Picture something the size of Jupiter but so light it could float on water. Sounds impossible, right? Yet that's exactly what astronomers have found orbiting a young star 352 light-years away—worlds so fluffy they're denser than carnival cotton candy by only a hair.
Welcome to FreeAstroScience.com, where we believe complex science belongs to everyone. Today, we're exploring one of the most exciting discoveries in exoplanet research: a family of four "cotton candy" planets that are teaching us how the most common worlds in our galaxy form and mature. This breakthrough, published in Nature in January 2026, represents nine years of patient observation—and it's rewriting what we know about planetary childhood .
If you've ever felt small looking up at the stars, this story will remind you that we're all connected to the same cosmic processes that shaped our own Earth billions of years ago. So grab your coffee, get comfortable, and let's journey together through this fascinating window into how planets grow up.
What Is V1298 Tau? Meet the Cosmic Kindergarten
A Star Still in Diapers
In the constellation Taurus, there's a star that's practically a newborn. V1298 Tau is only about 10–30 million years old . To put that in perspective: if our Sun were a 45-year-old adult, this star would be a 5-month-old baby.
Yet despite its youth, V1298 Tau already has four planets orbiting it. These aren't ordinary worlds. They're massive—ranging from Neptune-sized to Jupiter-sized—but astonishingly light. Think of a balloon the size of a house. That's essentially what we're looking at here.
Key facts about the V1298 Tau system:
| Property | Value |
|---|---|
| Distance from Earth | 352 light-years |
| System Age | 10–30 million years |
| Stellar Mass | 1.10 ± 0.05 solar masses |
| Number of Known Planets | 4 |
| Location | Taurus star-forming region |
This system was first spotted by NASA's Kepler space telescope during its K2 mission . What makes it special isn't just its youth. It's that we're catching these planets in a "turbulent and transformative" phase that most planetary systems have long since passed through V1298 Tau system serves as a "missing link" between protoplanetary disks—those swirling clouds of gas and dust where planets are born—and the mature systems that Kepler found scattered across our galaxy .
The Cotton Candy Mystery: Why Are These Planets So Fluffy?
Planetary Puffballs Defy Expectations
Here's where things get wild. When astronomers measured these planets, they found something that initially didn't make sense. The four worlds are huge—between 5 and 10 times Earth's radius—but weigh only 5 to 15 times what Earth weighs .
Do the math, and you get densities so low they're hard to imagine.
| Planet | Mass (M⊕) | Radius (R⊕) | Density (g/cm³) | Orbital Period |
|---|---|---|---|---|
| V1298 Tau c | 4.7 ± 0.6 | 5.08 ± 0.37 | 0.20 | 8.25 days |
| V1298 Tau d | 6.0 ± 0.7 | 6.53 ± 0.42 | 0.12 | 12.40 days |
| V1298 Tau b | 13.1 ± 5.3 | 9.41 ± 0.57 | 0.09 | 24.14 days |
| V1298 Tau e | 15.3 ± 4.2 | 10.17 ± 0.75 | 0.08 | 48.68 days |
*Data source: Livingston et al. 2026, Nature *
Let's put these numbers in context:
- Earth's density: 5.5 g/cm³
- Saturn (the least dense planet in our solar system): 0.69 g/cm³
- Cotton candy density: ~0.05 g/cm³
- The least dense V1298 Tau planet (e): 0.08 g/cm³
One of these planets—V1298 Tau e—is essentially the density of cotton candy from a carnival . Another has the density of a marshmallow. These are among the lowest-density exoplanets ever recorded .
If you dropped one of these worlds into a giant cosmic ocean (assuming one existed), it would float like a beach ball. The planetary densities measured in the V1298 Tau system are among the lowest ever recorded, comparable only to the famous "super-puff" planets of the Kepler-51 system .
How Do Scientists Weigh a Baby Planet?
The Challenge of a Hyperactive Star
Normally, astronomers weigh planets using a technique called "radial velocity." When a planet orbits a star, it tugs the star back and forth ever so slightly. We can measure this wobble and calculate the planet's mass.
But V1298 Tau threw a wrench into that plan.
Young stars are messy. They're covered in starspots. They flare constantly. All that activity creates noise that drowns out the tiny signal from orbiting planets . Previous attempts to measure these planets' masses using radial velocity gave estimates that were 200 to 300 times too high.
Imagine trying to hear a whisper at a rock concert. That's essentially the challenge here. The expected radial velocity signals from these planets are only about 1–2 m/s, but the stellar activity creates noise of 195–260 m/s .
Transit-Timing Variations: A Clever Workaround
So the research team, led by John Livingston of the National Astronomical Observatory of Japan, turned to a different method: transit-timing variations, or TTVs .
Here's how it works. When a planet passes in front of its star (a "transit"), it blocks a tiny bit of light. If there were only one planet, these transits would happen like clockwork, perfectly regular.
But when multiple planets orbit the same star, their gravitational pulls affect each other. Sometimes a planet speeds up a little. Sometimes it slows down. These tiny timing shifts—sometimes just minutes—reveal how much each planet weighs
The proximity to orbital resonance is described by:
Where P1 and P2 are the orbital periods of the inner and outer planets, and j defines the resonance. Smaller Δ values mean stronger interactions and larger TTVs .
The team gathered data from an impressive arsenal of telescopes over nine years:
- NASA's Kepler (K2 mission)
- NASA's TESS
- Spitzer Space Telescope
- Las Cumbres Observatory Global Telescope Network
- NAOJ's 188-cm telescope in Okayama
- MuSCAT, MuSCAT2, and MuSCAT3 instruments
- Apache Point Observatory
- And many more
That patience paid off. Not only did they get accurate masses, but they also "recovered" a previously lost planet—V1298 Tau e—whose orbital period had been uncertain. By 2022, the team's preliminary timing data revealed large TTVs for planet b that pointed toward a specific period for planet e. They predicted where planet e should transit and caught a partial transit from the ground in October 2022, confirming the 48.7-day orbital period .
The "Boil-Off" Phenomenon: When Planetary Lids Come Off
Why Are These Planets So Puffy?
Why are these planets so puffy in the first place? The answer lies in what happened right after they formed.
Planets form inside disks of gas and dust that swirl around young stars. Think of this disk as a "lid" that keeps everything contained. The disk's pressure holds a planet's atmosphere in place .
But young stars are violent. Eventually, they blow away their protoplanetary disk with intense radiation. When that happens, something dramatic occurs.
Imagine a pressure cooker. Inside, everything stays compressed because the lid keeps the pressure balanced. But remove the lid suddenly? Steam explodes outward.
That's essentially "boil-off" on a planetary scale .
When the protoplanetary disk disperses, a planet's atmosphere suddenly finds itself unconfined. It expands rapidly, carrying away internal heat and leaving the planet in a low-entropy state—cooler inside than traditional models would predict .
Evidence Written in Density
The research team found strong evidence that the inner two planets (c and d) went through this boil-off phase. How do we know?
Standard core-accretion models predicted that if planet c had a mass higher than 10 Earth masses, it would be consistent with normal formation. But if it had a mass lower than 6 Earth masses, it would require boil-off .
The measured mass? 4.7 ± 0.6 Earth masses .
That's a smoking gun.
The team's modeling showed that planets c and d require initial Kelvin-Helmholtz cooling timescales much greater than 30 million years—far longer than standard models predict. This is exactly what boil-off theory predicts .
From Fluff to Rock: What Will These Planets Become?
A Preview of Planetary Adolescence
These cotton candy worlds won't stay fluffy forever. Over the next few hundred million years, they'll shrink dramatically.
Two processes drive this transformation:
- Photoevaporation: The star's radiation slowly strips away atmosphere
- Core-powered mass loss: Heat from the planet's own interior pushes atmosphere outward
The team predicts these planets will contract from their current bloated sizes (5–10 Earth radii) down to 1.5–4.0 Earth radii .
When that happens, they'll join the two most common types of planets in our galaxy:
- Super-Earths: Rocky worlds with radii less than 1.5 times Earth
- Sub-Neptunes: Gassy worlds with radii around 2 times Earth
The Radius Valley Mystery—Solved?
Kepler discovered something puzzling: there's a "valley" in the distribution of planet sizes. Planets cluster either below 1.5 Earth radii or above 2 Earth radii. Very few exist in between .
This "radius valley" has stumped scientists. Why does nature avoid making planets of intermediate size?
V1298 Tau may hold the answer. These young planets are positioned above the radius valley right now . As they age and lose their atmospheres, some will shrink enough to cross the valley and become rocky super-Earths. Others will retain enough gas to become sub-Neptunes.
We're watching the origin story of the galaxy's most common planetary architectures in real-time.
| Current State (20 Myr) | Future State (~5 Gyr) |
|---|---|
| 5–10 Earth radii ("Cotton candy") | 1.5–4.0 Earth radii (Rocky/Gaseous) |
| Above the radius valley | Split into super-Earths and sub-Neptunes |
| H/He-rich atmospheres (10–20% by mass) | Thin or stripped atmospheres |
| Densities: 0.08–0.20 g/cm³ | Densities approaching terrestrial values |
The "Peas in a Pod" Pattern: A Cosmic Family Portrait
Siblings Look Alike—Even in Space
Here's something beautiful that emerged from the data. Despite their different sizes today, all four V1298 Tau planets likely started with remarkably similar properties .
The research team's modeling suggests:
- Similar core masses: All around 4–6 Earth masses
- Similar initial envelope fractions: About 10–20% of their mass in hydrogen/helium atmospheres
This matches a pattern astronomers have noticed in mature planetary systems: planets in the same system tend to be similar in size and regularly spaced, like "peas in a pod" .
What does this mean?
The current size diversity we see—planets ranging from 5 to 10 Earth radii—isn't a reflection of how they formed. It's a snapshot of different stages of atmospheric loss. The inner planets, closer to the star, are getting blasted more intensely and losing atmosphere faster .
Given enough time, their fates will diverge. But at birth? They were practically twins.
The system also shows nearly circular orbits (all eccentricities less than about 1%), implying a dynamically calm history—no violent gravitational encounters that would have scattered the planets into elongated orbits .
Why Should We Care? The Bigger Picture
Understanding Worlds We Can't Visit
You might wonder: these planets are 352 light-years away. We'll never go there. Why does this matter?
Here's why: super-Earths and sub-Neptunes are the most common type of planets in our galaxy About 30% of Sun-like stars have Kepler-like planetary systems . They're everywhere—except in our own solar system.
That's right. Earth, Mars, Venus, Mercury... none of them are super-Earths. Jupiter, Saturn, Uranus, Neptune... none of them are sub-Neptunes. Our solar system is the oddball.
Understanding how these common worlds form might explain why our cosmic neighborhood is so unusual. Did something different happen here? Did our early solar system avoid the conditions that produce super-Earths?
V1298 Tau gives us a living laboratory to test our theories.
The James Webb Connection
The story doesn't end with mass measurements. The James Webb Space Telescope observed V1298 Tau b's atmosphere, and the results were striking. A 2025 analysis of transmission spectra inferred a mass from the atmospheric scale height that is in excellent agreement with the TTV result .
Two completely independent methods—one based on gravitational dynamics, one on atmospheric physics—reached the same conclusion . That kind of agreement gives scientists confidence they're on the right track.
An Unresolved Mystery
Interestingly, the JWST observations suggested a high internal temperature for planet b, which might create some tension with the boil-off scenario that predicts cooler interiors . This puzzle shows that even as we answer some questions, new ones emerge. Science is never finished—it's always asking the next question.
What This Teaches Us About Our Place in the Universe
We've traveled 352 light-years today without leaving our seats. We've watched baby planets swaddled in hydrogen like cosmic cotton candy. We've learned how they'll grow up, shed their gaseous jackets, and become the rocky or gassy worlds that dominate our galaxy.
This is what science does. It connects us to processes we'll never see firsthand. It reminds us that we're made of the same atoms, forged in the same stellar furnaces, shaped by the same gravitational laws as those distant, fluffy worlds.
The V1298 Tau system teaches us three profound lessons:
Patience reveals truth. Nine years of observations, dozens of telescopes, and an international team of scientists were needed to weigh planets we can't touch.
Youth is transformative. These planets are caught in a fleeting moment of change—much like teenagers going through growth spurts—and will look completely different in a few billion years.
We're the exception, not the rule. Our solar system lacks the super-Earths and sub-Neptunes that fill the galaxy. Understanding V1298 Tau might help us understand why we're so cosmically unusual .
At FreeAstroScience.com, we believe that understanding these cosmic stories makes us more human, not less. When we learn how planets evolve, we learn something about change, about patience, about the way nature sculpts complexity from chaos over billions of years.
Never turn off your mind. Keep asking questions. Keep wondering about what's out there. Because the sleep of reason breeds monsters—but curiosity? Curiosity builds bridges to the stars.
This article was written specifically for you by FreeAstroScience.com, where complex scientific principles become simple conversations. Come back whenever you're ready for your next cosmic adventure. The universe isn't going anywhere, and neither are we.
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