---
title: DECam Rogue Earths & Mars Survey (DREAMS)
url: https://www.emergentmind.com/topics/decam-rogue-earths-and-mars-survey-dreams
type: topic
---

# DECam Rogue Earths & Mars Survey (DREAMS)

The DECam Rogue Earths and Mars Survey (DREAMS) is a high-cadence gravitational microlensing program operating on the Blanco 4 m telescope at CTIO since June 2025. Its primary objective is to extend microlensing sensitivity into the regime of extremely low-mass planetary bodies, targeting both bound analogs—"rogue Earths" in wide orbits—and unbound, free-floating planets (FFPs), with detection thresholds approaching the mass of Mars and, in favorable conditions, the Moon. DREAMS leverages minute-scale imaging cadence, a large-aperture telescope, and the wide field of view of the DECam imager to address parameter spaces inaccessible to conventional microlensing surveys, thus enabling statistical constraints on sub-Earth-mass planetary populations in the Galactic bulge and disk [2601.11469].

## 1. Scientific Motivation

DREAMS addresses both the detection of faint, low-mass bound exoplanets and the census of unbound planetary-mass objects. Traditional microlensing surveys (e.g., OGLE, MOA, KMTNet, PRIME) provide wide-area coverage (∼100 deg²) but are limited to cadences of at most ∼6 hr⁻¹, rendering them photon-starved for high-magnification, short-duration events characteristic of $q \lesssim 10^{-4}$ mass ratios or sub-Earth-mass FFPs. Previous studies (Sumi et al. 2011; Mroz et al. 2017; Gould et al. 2022) hint at a substantial FFP population below 1 $M_{\oplus}$, but Mars-mass ($M \lesssim 0.1 M_{\oplus}$) events—typically with Einstein crossing times $t_E \lesssim 0.5$ hr—remain at the limits of survey detectability. DREAMS’s approach fuses high temporal cadence (1–2 min), millimagnitude photometric precision, and focused Galactic bulge fields, thereby enabling the detection of FFPs down to $\sim$0.03 $M_{\oplus}$ and bound systems at extremely low mass ratios.

## 2. Instrumentation and Technical Configuration

DREAMS utilizes the Blanco 4 m telescope at CTIO, configured with an f/2.7 prime focus. The Dark Energy Camera (DECam) provides a $3\,\mathrm{deg}^2$ field of view across 62 science CCDs with a pixel scale of $0.263^{\prime\prime}$ per pixel. Observations are conducted in SDSS-like $r$ and $z$ filters, optimizing for the extinction properties and expected source colors in the bulge. These instrumental specifications are critical to supporting minute-cadence, high-precision photometric monitoring across the selected fields [2601.11469].

## 3. Survey Design and Observing Strategy

The primary fields encompass $5\,\mathrm{deg}^2$ in the Galactic bulge, selected for moderate extinction ($A_I$ and $E(V–I)$) and elevated microlensing event rates, with longitude and latitude ranges $\ell \sim -1$ to $+2^{\circ}$, $b \sim -2.8$ to $-0.6^{\circ}$. The 2025 "pilot I" campaign (June 29–July 4) implemented five $z$-blocks ($4 \times 42$ s exposures) plus one $r$-block ($4 \times 60$ s) per hour per field, totaling 20 $z$ and 4 $r$ exposures hr⁻¹. The "pilot II" (September) run adjusted to four $z$-blocks ($4 \times 60$ s) and one $r$-block ($3 \times 80$ s) per hour. The long-term (2026–2028) baseline calls for two adjacent, partially overlapping fields sampled with four $z$-blocks ($4 \times 60$ s) and one $r$-block (80 s) per hour over $\sim$30–40 nights per bulge season.

| Component             | Specification                                               | Purpose/Benefit                         |
|-----------------------|------------------------------------------------------------|-----------------------------------------|
| Blanco 4 m            | f/2.7 prime focus                                          | Large aperture for faint source recovery|
| DECam                 | $3\,\mathrm{deg}^2$, 62 CCDs, $0.263^{\prime\prime}$/pixel | Wide field, high spatial resolution     |
| Filters               | SDSS-like $r$, $z$                                         | Mitigate extinction, sample source color|
| Cadence               | 1–2 min exposures                                          | Capture short-duration FFP events       |

## 4. Photometric Reduction, Calibration, and Performance Metrics

DECam raw frames are processed by the NOIRLab DECam Community Pipeline (bias, flat-field, cross-talk, WCS correction). Difference-image analysis (DIA) is conducted via pySIS (for KMTNet and DREAMS) and PRIME’s custom pipeline. For each source $i$ and time $t$:
$$
f_i(t) = f_{S,i} A(t) + f_{B,i}
$$
where $A(t)$ is the microlensing magnification (computed via VBBinaryLensing), $f_{S,i}$ the source flux, and $f_{B,i}$ blend flux. Error normalization follows Yee et al. (2012): $\chi^2/\mathrm{dof} \approx 1$ for non-variable stars.

The empirically determined signal-to-noise relationships are:
- $SNR_z(m_z) \simeq 26.5 \times 10^{(18.4-m_z)/2.5}$
- $SNR_r(m_r) \simeq 14.7 \times 10^{(19.4-m_r)/2.5}$

For a 60 s $z$-band exposure at $z=18.4$, $SNR\approx 26.5$ ($\sigma \approx 0.04$ mag). In the September 2025 pilot, DREAMS achieved $\sim$0.04 mag rms at $z\approx18.4$ and $\sim$0.07 mag rms at $r\approx 19.4$, defining 3$\sigma$ finite-source FFP detection limits for duration $\lesssim$10 min at Mars mass for typical bulge parameters, or Moon mass ($\lesssim 0.03 M_\oplus$) in favorable (low extinction or overlap) regions.

## 5. Early Discovery: KMT-2025-BLG-1616Lb

The high-magnification ($A_{max}\approx1300$) microlensing event KMT-2025-BLG-1616 was independently detected by KMTNet and DREAMS. KMTNet data presented a short U-shaped anomaly near maximum, but binary-lens model solutions (central versus resonant caustics) were highly degenerate ($\Delta\chi^2 \lesssim 1$). DREAMS minute-cadence $z$ and $r$ data resolved this, significantly preferring the "wide-resonant" solution ($s \approx 1.068$, $q \approx 4.9 \times 10^{-4}$, $\Delta\chi^2\approx 330$ over central models). DREAMS provided precise source color via time-correlated $r$–$z$ blocks:
- $(r-z)_S = 1.212\pm0.006$ (DECam)
- $(V-I)_S = 3.106\pm0.016$ (transformed)
- Extinction-corrected $I_{0,S}=19.66\pm0.06$, $(V-I)_{0,S}=0.96\pm0.04$
- Angular source size $\theta_*=0.470\pm0.026$ μas
- Normalized source radius $\rho \approx 2.18\times10^{-3}$
- Einstein radius $\theta_E=0.216\pm0.014$ mas, relative proper motion $\mu_{rel}=9.8\pm0.7$ mas yr⁻¹

Bayesian Galactic-model analysis yields:
- $M_{host} = 0.26^{+0.25}_{-0.14}M_\odot$
- $M_{planet} = 42^{+41}_{-22} M_\oplus$
- $D_L = 7.5^{+0.7}_{-1.0}$ kpc
- $a_\perp \simeq 1.6^{+0.2}_{-0.3}$ au

This constitutes the first bound-planet detection from DREAMS and demonstrates the scientific advantage of high-cadence sampling in degeneracy resolution [2601.11469].

## 6. Sensitivity to Free-Floating Planets: Simulations and Thresholds

DREAMS sensitivity to sub-terrestrial-mass FFPs has been quantified through end-to-end simulation of point-lens, finite-source light curves using the post-2025 cadence. For a bulge Mars-mass FFP ($M_L=0.107\,M_\oplus$, $D_L=7.0$ kpc, $D_S=8.5$ kpc, $\mu_{rel}=6.5$ mas yr⁻¹), sources at $I=18.0, 19.5, 20.5$ mag with photometric noise and extinction ($A_I=1.8$, $E(V-I)=1.55$) satisfy detection criteria:
1. At least six data points exceed baseline by $\geq$3$\sigma$
2. $\Delta\chi^2 = \chi^2_{\rm flat} - \chi^2_{\rm best(1L1S)} \geq 300$

For a disk Moon-mass case ($M_L=0.0123\,M_\oplus$, $D_L=3.2$ kpc, $D_S=8.5$ kpc, $\mu_{rel}=8$ mas yr⁻¹, source $I=19.5$), simulated events yield ten points $>3\sigma$, $\Delta\chi^2\approx370$, confirming sensitivity to $M \lesssim 0.03\,M_\oplus$ lenses. Cadence overlap within the $1\,\mathrm{deg}^2$ intersection further enhances this capability.

## 7. Role in Broader Exoplanet Demographics and Prospects

DREAMS fills a niche in exoplanet microlensing by:
- Detecting faint, low-mass bound exoplanets inaccessible to wider, slower surveys;
- Achieving, for the first time, robust sensitivity to Mars- and Moon-mass FFPs;
- Enabling color measurement of extremely faint sources ($I > 22$) via multi-band, high-cadence data.

Over the 2026–2028 bulge seasons, DREAMS will collect tens of thousands of DECam exposures across $\sim$10 deg² at minute cadence, facilitating a statistical census of terrestrial-mass and sub-terrestrial-mass rogue planets and extending bound-planet detection toward $q \sim 10^{-5}$. When combined with KMTNet, OGLE, MOA, PRIME, and anticipated space-based missions (Roman, Euclid), DREAMS is poised to support a nearly comprehensive mapping of galactic planetary demographics from gas giants through Moon-mass wanderers [2601.11469].

Source: https://www.emergentmind.com/topics/decam-rogue-earths-and-mars-survey-dreams