---
title: 'TOI-451: Young Multi-Planet System'
url: https://www.emergentmind.com/topics/toi-451-planetary-system
type: topic
---

# TOI-451: Young Multi-Planet System

The TOI-451 planetary system is a benchmark young multi-planet system composed of a G8 V primary (TOI 451) and three validated transiting planets, with a co-moving wide binary M-dwarf companion and a debris disk. The primary star is a confirmed member of the 120–125 Myr-old Pisces–Eridanus (Psc–Eri) stream, making the system a key laboratory for probing planetary formation and atmospheric evolution processes at an early epoch. Initial discovery was accomplished through TESS photometry, with confirmation via Spitzer, ground-based facilities, and ESPRESSO radial velocities, using multidimensional Gaussian Process (GP) frameworks that leverage contemporaneous photometric and spectroscopic activity indicators [2102.06049, 2601.09438, 2103.09746].

## 1. Stellar Properties and Age

TOI 451 (TIC 257605131) is characterized as a G8 V star with $T_{\mathrm{eff}} = 5490 \pm 115$ K, [Fe/H]$ = +0.02 \pm 0.06$, $M_{\star} = 0.93 \pm 0.04 \, M_{\odot}$, and $R_{\star} = 0.85 \pm 0.03 \, R_{\odot}$, placing it slightly below solar mass and radius [2601.09438]. The system’s age is kinematically and chemically constrained at $125 \pm 8$ Myr, consistent with the Psc–Eri stream and with lithium abundance $A({\rm Li}) = 2.80\pm0.10$ dex, UV excess, rapid rotation ($P_{\rm rot} = 5.1 \pm 0.1$ d, $v\sin i = 8.7 \pm 0.96$ km s⁻¹), and chromospheric activity [2102.06049]. The star exhibits photometric amplitudes of 1–2%, and its kinematics match the stream with $(U,V,W) = (-10.92, -4.18, -18.81) \pm (0.05, 0.08, 0.09)$ km s⁻¹ [2102.06049]. Membership probability in Psc–Eri is estimated at $\sim$97%.

## 2. Planetary Architecture and Orbital Parameters

The system contains three transiting planets, TOI-451 b, c, and d. Their orbital and transit parameters, as refined by simultaneous modeling of multiple TESS campaigns and ground-based photometry, are summarized below.

| Parameter           | TOI-451 b           | TOI-451 c            | TOI-451 d           |
|---------------------|---------------------|----------------------|---------------------|
| Period $P$ (d)      | $1.8586273\pm0.0000012$ | $9.1926242\pm0.0000044$ | $16.364881\pm0.0000085$ |
| $R_p$ ($R_\oplus$)  | $1.71\pm0.08$       | $2.96\pm0.12$        | $3.92\pm0.12$       |
| $a$ (AU)            | $0.0272\pm0.0006$   | $0.0745\pm0.0010$    | $0.1056\pm0.0015$   |
| Inclination (deg)   | $87.14\pm0.29$      | $89.06\pm0.17$       | $88.34\pm0.14$      |
| Impact param. $b$   | $0.64\pm0.04$       | $0.26\pm0.04$        | $0.43\pm0.06$       |

Ephemerides have been refined using joint pyaneti modeling and all available TESS data, yielding mid-transit times with $\sigma_{T_0} \lesssim 3$ minutes; the periods are stable to $<10^{-5}$ d [2103.09746, 2601.09438].

## 3. Mass Determinations and Bulk Compositions

Radial velocities from ESPRESSO, modeled with a two-dimensional “multi-GP” approach that incorporates contemporaneous NGTS/LCO photometry as an activity indicator, yield Doppler semi-amplitudes:

- $K_b = 2.8\pm1.1$ m s⁻¹
- $K_c = 1.4^{+1.2}_{-0.9}$ m s⁻¹
- $K_d = 2.9\pm1.4$ m s⁻¹

Inferred planet masses and $2\sigma$ upper limits:

| Planet   | $M_p (M_\oplus)$      | $2\sigma$ Upper Limit ($M_\oplus$) |
|----------|----------------------|-------------------------------------|
| b        | $5.0\pm1.9$          | $<9.7$                              |
| c        | $3.1\pm2.7$          | $<11.5$                             |
| d        | $9.7\pm3.6$          | $<20.7$                             |

Bulk densities are $4.8\pm2.2$ g cm⁻³ (b), $1.2\pm1.0$ g cm⁻³ (c), $1.25\pm0.58$ g cm⁻³ (d), indicating that c and d require substantial H/He envelopes ($\sim$5–8% by mass if Earth-like core), while b may be a rocky planet retaining a tenuous H/He layer or a water-dominated body [2601.09438]. The orbital spacing and period ratios do not strongly suggest resonant behavior, but transit-timing variations (TTVs) at the $\sim0.5$–2 min level are predicted (between c and d over $\sim$75 d timescales) [2102.06049].

## 4. Photometric and Radial Velocity Methodologies

Light curves from TESS (Cycles 1 and 3), NGTS, and LCO were detrended for stellar variability using a quasi-periodic Gaussian Process kernel:

$$
k(t, t') = A^2 \exp\left[-\frac{(t-t')^2}{2\lambda_e^2} - \frac{\sin^2[\pi (t-t')/P_{\mathrm{GP}}]}{2\lambda_p^2}\right]
$$

Photometric time series provide direct constraints on stellar rotation ($P_{\mathrm{GP}}\sim5.13$–5.18 d) and the active-region evolution timescale ($\lambda_e$), as well as priors on the quasi-periodic activity kernel used for RV joint modeling [2601.09438, 2103.09746]. This methodology robustly disentangles planetary signals from chromospheric activity, which is essential in young, rapidly rotating stars where RV jitter is typically significant.

## 5. Stellar Environment: Debris Disk and Wide Binary Companion

TOI 451 exhibits infrared excesses in WISE W3 (26 ± 7%) and W4 (70 ± 30%) bands, statistically significant at 3.7σ and 2.3σ, indicative of a debris disk with inferred temperatures $<$ 300 K [2102.06049]. The co-moving wide companion TOI 451 B (TIC 257605132) has $T_{\mathrm{eff}}\sim3500$ K (M3V), lies at a projected separation of 37.8″ ($\sim4700$ AU), and is itself likely an unresolved near-equal mass binary (Gaia RUWE = 1.24, $M_{B,\rm total}\sim0.45\,M_{\odot}$). The wide binary architecture and presence of a debris disk are consistent with early dynamical stability and ongoing planetary system dynamical processes.

## 6. Atmospheric Characterization and Evolutionary Implications

Atmospheric transmission signals are predicted to be $\Delta D \approx$ 260 (b), 460 (c), and 760 (d) ppm; scale heights are $H \sim$ 4000–5500 km, assuming $\mu=2.3m_p$ and measured $T_{\mathrm{eq}}$ values [2102.06049]. Transmission Spectroscopy Metric (TSM) values place c and d among the top $\sim5\%$ of small planets for atmospheric follow-up with JWST. All three planets offer prospects for measuring atmospheric loss via helium 10 830 Å absorption, especially in the context of post-peak high-energy irradiation for $\tau\sim125$ Myr [2601.09438]. Both photoevaporation and core-powered mass-loss processes may be ongoing; TOI-451 planets provide a rare window onto processes sculpting the radius valley at early evolutionary times.

## 7. Prospects and Future Directions

The TOI-451 system supports high-cadence photometry (e.g., PLATO), intensive RV campaigns ($>125$ ESPRESSO epochs across five months recommended), and transmission and emission spectroscopy campaigns with JWST and HST. Precise monitoring of stellar activity remains critical for RV disentanglement; the system's rapidly evolving spot coverage and active-region lifetimes were directly observed to change over two-year timescales. The system's well-determined age, non-resonant compact multi-planet architecture, and the presence of a debris disk and wide binary companion provide essential boundary conditions for testing planet formation, migration, tidal evolution, and mass-loss modeling [2103.09746, 2601.09438].

A plausible implication is that TOI-451 serves as a reference point for comparative studies of sub-Neptune/super-Earth evolution and photoevaporation in young systems, informing demographic and atmospheric studies as observational precision improves. This makes TOI-451 an archetype for dynamical and atmospheric studies at the boundary of the radius valley in a post-disk, but still strongly irradiated, stellar environment.

Source: https://www.emergentmind.com/topics/toi-451-planetary-system