🔭 astrophysics

Stellar Obliquities of Young Systems, Atmospheres Undergoing Contraction and Escape (SOYSAUCE) II: a 135 Myr planet on an aligned orbit with transit timing variations

The paper "SOYSAUCE II" presents a 135 Myr-old exoplanet characterized by an aligned stellar obliquity and observed transit timing variations, contributing to the study of young planetary systems undergoing atmospheric contraction and escape.

Original authors: Madyson G. Barber, Andrew W. Mann, Sydney Vach, Leah J. Boff, Andrew W. Boyle, Andrew Vanderburg, Adam L. Kraus, Benjamin M. Tofflemire, Marshall C. Johnson, Allyson Bieryla, David W. Latham, Karen A.

Published 2026-06-10

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Madyson G. Barber, Andrew W. Mann, Sydney Vach, Leah J. Boff, Andrew W. Boyle, Andrew Vanderburg, Adam L. Kraus, Benjamin M. Tofflemire, Marshall C. Johnson, Allyson Bieryla, David W. Latham, Karen A. Collins, Steve B. Howell, Richard P. Schwarz, Gregorg Srdoc, Francis P. Wilkin, Felipe Murgas, Enric Palle, Chris Stockdale

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the universe as a giant, bustling nursery. Most of the planets we know are like adults in their 30s or 40s—stable, settled, and easy to study. But astronomers are rarely able to catch a glimpse of the "teenage" phase of planets, those that are roughly 100 to 500 million years old. This is a critical time when planets are still growing, shedding their baby atmospheres, and figuring out their final orbits, but they are notoriously difficult to find because their host stars are still very active and "moody," making them hard to watch.

This paper, titled SOYSAUCE II, is like a detective story about a specific teenage planetary system named TIC 150070085. Here is the breakdown of what the researchers found, using simple analogies:

1. The Target: A Teenage Star and Its Planets

The team focused on a star called TIC 150070085. By studying the star's neighborhood (a group of stars born together called Alessi 84), they determined the star is 135 million years old. Think of this as the star being in its "high school" years.

They found two planets orbiting this star:

Planet b: The confirmed star of the show. It's a "sub-Neptune" (about 3.6 times the size of Earth) that orbits the star every 10.5 days.
Planet c: A "suspect" or candidate. It's slightly smaller (3 times Earth's size) and orbits every 15.9 days. While they couldn't fully confirm it yet, the evidence strongly suggests it's real.

2. The "Dance" Between the Planets

The two planets are very close to a 3:2 resonance. Imagine two dancers on a floor. If one takes 3 steps, the other takes 2. They are almost perfectly in sync, but not quite.

Because they are so close to this rhythm, they tug on each other gravitationally. This causes Transit Timing Variations (TTVs).

The Analogy: Imagine a train that is supposed to arrive at the station exactly at 5:00 PM every day. However, because another train is passing by on a parallel track and pulling on it, the first train arrives 30 minutes early one day and 30 minutes late the next.
The Result: The researchers saw Planet b arriving at its "station" (passing in front of the star) at times that were off by about 30 minutes. This "wobble" in the schedule is the smoking gun that proves a second planet (Planet c) is there, even though they haven't seen Planet c transit the star clearly yet.

3. The "Spin" Check: Are They Aligned?

One of the biggest questions in astronomy is: Do planets orbit their stars in the same direction the star is spinning?

The Analogy: Think of a star as a spinning top. If a planet orbits in the same direction the top is spinning, it's "aligned." If it orbits sideways or backwards, it's "misaligned."
The Finding: The researchers used a special instrument called MAROON-X to watch the star's light shift as the planet passed in front of it (an effect called the Rossiter-McLaughlin signal). They found that Planet b is mostly aligned with its star. The angle of misalignment is very small (about 18 degrees).
Why it matters: This supports the idea that young planets tend to be well-behaved and aligned, only getting "messy" or misaligned later in life due to chaotic collisions or gravitational tugs from other stars.

4. Why This Discovery is Special

Finding planets in this specific age range (around 100–135 million years) is like finding a rare fossil.

The Gap: We have plenty of data on brand-new planets (infants) and old planets (adults), but the "adolescent" phase is a black box.
The Contribution: This paper fills in a gap. It shows us a system that is old enough to have settled down a bit, but young enough that we can still see the effects of its formation. It confirms that young planetary systems can be stable and aligned, helping scientists build a timeline of how solar systems grow up.

Summary

In short, the authors found a 135-million-year-old star with a confirmed planet and a likely second planet. The two planets are playing a gravitational game of tag that causes the first planet to arrive early or late. The first planet is orbiting in the same direction the star spins, suggesting that young planetary systems are generally orderly. This discovery helps astronomers understand the "teenage years" of planet formation, a phase that is usually too hard to see.

Technical Summary: SOYSAUCE II – A 135 Myr Planet on an Aligned Orbit with Transit Timing Variations

Problem Statement
Young planetary systems (<1 Gyr) offer a unique window into planet formation and evolution, yet the "adolescent" population (∼100–500 Myr) remains poorly characterized due to heightened stellar activity which complicates detection and validation. Furthermore, the current sample of young planets with measured spin-orbit obliquities is too small and inhomogeneous to definitively determine whether misalignments are primordial or acquired through secular processes. There is a critical need to bridge the gap between planetary infancy (<50 Myr) and maturity (>1 Gyr) by validating and characterizing systems in this intermediate age regime, particularly multi-planet systems where Transit Timing Variations (TTVs) can constrain masses in the presence of stellar jitter.

Methodology
The authors present the validation and characterization of TIC 150070085 b and a candidate signal, TIC 150070085 c, using a multi-faceted approach:

Photometry and Transit Detection: TESS data (Sectors 20 and 47) were re-analyzed using the Notch & LOCoR search algorithm to recover the primary 10.47-day signal and identify a secondary 7.9-day candidate. Ground-based follow-up was conducted using LCOGT (1m telescopes) and the Teide Observatory (0.4m and 1m telescopes) to confirm transits and measure Transit Timing Variations.
Spectroscopy and Stellar Characterization: High-resolution spectra were obtained from TRES, LCOGT-NRES, and MAROON-X. Stellar parameters ( $T_{\text{eff}}$ , $\log g$ , $v \sin i_*$ , metallicity) were derived via Stellar Parameter Classification (SPC) and Spectral Energy Distribution (SED) fitting.
Age Determination: The host star's membership in the Alessi 84 association was confirmed using the FriendFinder algorithm to identify co-moving stars. The cluster age was refined by combining isochronal modeling (PARSEC and DSEP-mag), gyrochronology (using the TARS catalog), and variability-based age estimation (EVA).
Rossiter-McLaughlin (RM) Analysis: A transit observation with MAROON-X was analyzed to measure the sky-projected obliquity ( $\lambda$ ) using an updated MISTTBORN implementation, simultaneously fitting photometric and radial velocity data.
Validation: False-positive probabilities were assessed using TRICERATOPS, speckle imaging ('Alopeke), and the presence of TTVs.

Key Results

System Validation: TIC 150070085 b is validated as a planet with a radius of $3.62^{+0.21}_{-0.20} R_\oplus$ on a 10.47-day orbit. The False Positive Probability (FPP) is <0.009.
Candidate Planet: A candidate signal, TIC 150070085 c, is detected with a period of 15.90 days ( $3.03^{+0.30}_{-0.26} R_\oplus$ ). While the FPP is <0.001, the signal remains a candidate pending further transit confirmation due to a data gap in TESS Sector 47 coinciding with the expected transit.
Stellar Age and Properties: The host star is confirmed as a member of Alessi 84. By combining isochronal, gyrochronological, and variability methods, the age of the system is updated to 135 ± 10 Myr. The host star has $T_{\text{eff}} \approx 6000$ K, $M_* \approx 1.16 M_\odot$ , and a rotation period of 2.89 days.
Spin-Orbit Alignment: The RM analysis yields a sky-projected obliquity of $|\lambda| = 18 \pm 12^\circ$ . The true 3D obliquity is estimated at $\psi = 23 \pm 11^\circ$ . This indicates the planet is on a near-aligned orbit with its host star.
Transit Timing Variations: The system exhibits TTVs with an amplitude of $\gtrsim 30$ minutes. The period ratio of the two planets is close to the 3:2 mean-motion resonance. TTVFast modeling suggests the TTVs are consistent with a system where planet c has a mass of $\sim 30 M_\oplus$ and planet b has a mass of 5–10 $M_\oplus$ .
Mass Limits: Radial velocity data from TRES, LCO, and MAROON-X constrain the mass of TIC 150070085 b to an upper limit of $1.1 M_J$ (95% confidence), ruling out stellar-mass companions.

Significance
This work contributes a crucial data point to the sparse population of transiting planets around stars aged 100–200 Myr. The system joins a small cohort of young planets with measured obliquities, reinforcing the pattern that young systems tend to be well-aligned ( $|\lambda| \lesssim 20^\circ$ ), in contrast to the broader population of mature systems which includes a significant fraction of misaligned orbits. The detection of significant TTVs in a young, active system demonstrates that dynamical interactions can be probed even when traditional radial velocity mass determinations are hindered by stellar activity. The validation of TIC 150070085 b and the identification of its resonant companion provide a laboratory for testing models of disk-driven migration and early planetary system architecture.

1. The Target: A Teenage Star and Its Planets

2. The "Dance" Between the Planets

3. The "Spin" Check: Are They Aligned?

4. Why This Discovery is Special

Summary

More like this