TKS Ephemeris · research · stellar encounter · Level 1 (star-only)

1.3 Million Years From Now — GJ 710 is projected to pass within the Hills-cloud region

GJ 710 = HIP 89825 = HD 168442 (K7Vk, V = 9.66) is the closest known future stellar encounter of the Solar System. Its proper motion is almost zero — the star is coming at us almost exactly head-on, at −14.47 km/s (Gaia DR2 radial velocity) from 62.3 ly (19.09 pc). This page propagates its full 6D astrometric state (Gaia EDR3 position · proper motion · parallax + radial velocity) in 3D, solves the closest approach (with a Monte-Carlo uncertainty band), the exact two-body encounter orbit, and the Oort-cloud impulse — and then validates itself independently against the published flyby (Gaia-DR1/DR2/EDR3 literature and ESA/Gaia material), including an explicit RV-sensitivity test of the two published radial-velocity zero-points. Star-only: no Galactic potential, no planets (that is Engine C, Level 2/3) — the honest limits are stated at the end.

Closest approach

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—epoch tc (Myr from J2000)
—minimum distance b
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Relative velocity & geometry

two-body
—relative speed (km/s)
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Oort cloud

scale
—b ÷ Hills-cloud inner edge (2,000 AU)
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RV sensitivity — two published radial-velocity zero-points

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The radial velocity is the largest single term of the relative velocity here (vt is only ~0.04 km/s), so a disagreement of 0.56 km/s between two published determinations moves the million-year extrapolation by ~4 % in both epoch and distance. Choose the zero-point above; the page recomputes everything. ESA/Gaia material quotes ≈ −14.53 km/s, i.e. in the Gaia-DR2 family rather than the 2026 re-determination.

Distance from the Sun — d(t)

log scale
x: time (kyr / Myr from J2000) · y: heliocentric distance (AU, log). Dashed horizontals: Hills (inner) cloud 2,000 AU, outer cloud 20,000 / 100,000 / 200,000 AU. The gold marker is the closest approach.

Independent validation — TKS vs published

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Encounter geometry — straight line vs exact two-body

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Both rows use the same input state; the difference is whether the mutual gravity of Sun + GJ 710 is included. At ~10,500 AU the gravitational focus shifts the closest-approach distance by only a few AU — so linear propagation is an excellent approximation here, unlike for encounters below a few hundred AU.

Position & brightness — what will be seen

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Trajectory (top view) — log-radius, Sun at centre

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Radial scale is logarithmic (same convention as the usual Oort-cloud diagrams), so the 19 pc start compresses into a straight chord. Rings: Hills cloud 2,000–20,000 AU, outer cloud 20,000–200,000 AU. The straight line is the unperturbed (linear) path over the selected span; the gold dot is the closest approach.

Apparent magnitude & proper motion

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V magnitude from the inverse-square law on the propagated distance (no extinction, no photometric model). Below V ≈ 6 the star becomes naked-eye; at closest approach it rivals the brightest planets.

Uncertainty — Monte-Carlo over Gaia astrometry

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Histogram of the closest-approach distance b over the Monte-Carlo samples (σ from Gaia EDR3: μα* ± 0.019, μδ ± 0.017 mas/yr, ϖ ± 0.0171 mas; RV as selected). Because the approach is nearly radial, b ∝ 1/|vr| × vt — the whole encounter distance rides on the tiny transverse velocity, i.e. on the proper motion. The pre-Gaia error bars were ~10–30× larger: their band is drawn for comparison.

Oort-cloud impulse Δv(r, ψ)

impulse approx.
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A comet on a shell of radius r feels the differential (tidal) pull of the passing star — the Sun's own acceleration is subtracted. Computed by numerically integrating the impulse along the star's straight path (fixed test particle, no orbital motion). Caveat: when the comet lies within a few 10² AU of the trajectory the impulse approximation over-predicts; those shells are marked. ψ = angle between the comet's position and the trajectory.

Level 2 · Engine C — Galactic encounter dynamics

querying /v1/tks/gj710 …
… loading the server-side Galactic integration …
propagates the Gaia σ through the full Galactic comparison — ~0.3 s
Server-side (/v1/tks/gj710): the Sun and GJ 710 are integrated in a common Milky-Way potential (bulge + Miyamoto–Nagai disk + NFW halo, own Dopri5 — no external library), then compared with the straight line, the exact two-body solution and the linearised Galactic tide. This is the question Engine C exists to answer: is the Galactic term bigger or smaller than the measurement error? The integration uses the radial velocity selected above, and is re-run whenever you switch it.

Estimate history — how the flyby converged

literature
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Same star, same question, twenty-five years: the encounter distance fell by a factor ≈ 7 as astrometry improved. The 2022 Gaia-EDR3 value and this page agree to better than 1 % — that agreement is the point of the validation card above, not a claim that the future is certain.

Input state — 6D Gaia astrometry

SIMBAD · Gaia EDR3
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μα* = μα·cos δ convention; epoch J2000 / ICRS. Provenance: parallax + proper motion Gaia EDR3 (2020yCat.1350....0G), radial velocity Soubiran et al. 2018 (Gaia DR2) — all values as carried by SIMBAD for HIP 89825; mass from Fernández-Puig et al. 2026.

Method, model limits and references

honest scope
What this page claims: from the published Gaia EDR3 position/proper-motion/parallax plus the published radial velocity, the linear 3D propagation of GJ 710 puts its nearest approach at t ≈ 1.29 Myr at b ≈ 10,533 AU, i.e. projected to pass within the Hills (inner) region of the Oort cloud, with a relative speed of ≈ 14.5 km/s; the exact two-body solution of the same state changes b by ~7 AU (0.06 %). The encounter is moderate, not catastrophic: the Sun itself gains only ≈ 7 m/s ( = 2GM*/bv, confirmed by the two-body deflection angle), and Oort-cloud comets gain a few m/s (strong only for objects within a few 100 AU of the trajectory).
What this page does NOT do (Level 1, star-only): no Galactic potential (Engine C → Level 2/3), so the Sun's and the star's Galactic orbits are ignored; no planets (their phase is meaningless over 106 yr); no extinction/photometric model; no comet dynamics (the impulse estimate freezes the comet); the Sun's reflex motion and GJ 710's own Galactic acceleration are omitted. Differing radial velocities (2026 literature gives −13.905 km/s) move the epoch by ~4 % and the distance by ~4 % — switchable above.

References. Gaia Collaboration (2021, EDR3) — parallax & proper motion; Soubiran et al. (2018, A&A 616 A7) — Gaia DR2 radial velocity; Fernández-Puig et al. (2026) — stellar parameters & RV; Berski & Dybczyński (2016, A&A 595 L10, IAU GA Focus Meeting 17) — Gaia-DR1 flyby; de la Fuente Marcos & de la Fuente Marcos (2018, RNAAS 2, 30) — Gaia-DR2 confirmation; de la Fuente Marcos & de la Fuente Marcos (2022, RNAAS 6, 136) — Gaia-DR3 update (0.051 pc); Dybczyński, Berski, Tokarek, Podlewska-Gaca, Langner & Bartczak (2022, A&A 664 A123) — StePPeD Gaia-EDR3 perturber catalogue 155 stars, 2 pc threshold, Monte-Carlo uncertainties; García-Sánchez et al. (2001, A&A 379, 634) — early estimate (0.34 pc); Jimenez-Torres et al. (2011, MNRAS 418, 1272) — full Galactic potential model (0.34 pc @ 1.36 Myr, pre-Gaia astrometry); Kaib & Raymond (2026, PSJ, arXiv:2606.25069) — comet-shower signature of the past HD 7977 passage; Oort-cloud structure (2,000–200,000 AU, Hills inner cloud) as reviewed in the standard literature.

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